National statistics

National Travel Survey 2022: Technical report chapter 4

Published 30 August 2023

Applies to England

Chapter 4: Fieldwork Procedures and Response Rate

4.1 Introduction

The NTS is a continuous survey with fieldwork taking place throughout the year, which has historically operated using a face-to-face (F2F) design since its inception. The methodological approach for NTS was altered in response to COVID-19 to ensure fieldwork could continue during the height of the pandemic and beyond in such a way as to minimise the effect on data quality and the time series as much as possible. These changes are outlined in full in Chapter 1 and summarised below for 2022 fieldwork.

Two modes of recruitment were used during 2022. Throughout the year, traditional doorstep recruitment was used wherever possible, which was preceded by the interviewers sending out an advance letter as usual. However, for any points (assignments) that could not be covered by an interviewer, the push-to-telephone (P2T) approach was used whereby sampled addresses were sent letters to voluntarily opt into the study (that is, no interviewer involvement in the recruitment stage). Households that wanted to participate were prompted to provide basic contact information via a freephone number or an online portal. The opt-ins were then re-grouped into new points (assignments) which contained a maximum of ten addresses. Interviewers then contacted the opt-ins via the phone numbers the households provided to arrange a telephone interview.

During quarter one, interviewing was conducted via telephone only. Interviewers used the pre-existing Computer-Assisted Personal Interviewing (CAPI) program developed during the pre-pandemic F2F years, with only minor program alterations to account for remote data collection by telephone. The combination of doorstep recruitment and telephone interviewing, known as knock-to-nudge (K2N), was the primary approach used (supplemented by P2T where necessary, as noted above). This involved interviewers making in-person contact with selected address with the intention of setting up a telephone interview. Interviewers were able to encourage selected addresses to take part in the survey through their doorstep interactions and then book an appointment with them to begin the interview process. They were also able to complete dwelling unit and household selection for situations when more than one dwelling unit or household existed at the address that was sampled from the Postcode Address File (see section 3.8 for more details).

Having made an appointment with a responding household, interviewers would complete the placement interview over the phone and begin populating the travel records (diaries) on the respondent’s behalf as per the ‘rolling travel weeks’ allocation approach. This approach stipulated that the travel week start date for the diaries was set, as standard, as the day before the interview, and was introduced during the pandemic to help facilitate telephone interviewing during this period. Interviewers would further populate the diaries via mid-week telephone calls with the responding household and at the pick-up interview (also conducted by phone). Interviewers would aim to make two mid-week calls (rather than one which was the approach pre-pandemic) to break down the task of populating the diaries into smaller and more manageable portions. All respondents were given memory joggers as standard to help recall their travel details during calls with their interviewer.

Aside from the recruitment and dwelling unit and household selection stages, P2T followed the same approach as K2N. This meant that P2T did not benefit from interviewers interacting with households to maximise.

From quarter two onwards, face-to-face (F2F) interviewing was reintroduced to the NTS as the primary fieldwork approach (also supplemented by P2T where necessary), effectively replacing K2N. This also meant a return to respondent completed travel records (diaries) and the traditional ‘fixed travel weeks’ allocation method, whereby interviewers provide a household with a specific week in which to record their travel in the diary. This methodical allocation process was designed to ensure a relatively even spread of travel week start days over (a) the dates of the month and (b) the days of the week, due to the random element that was central to the allocation method. As per the traditional fixed travel week approach, the first travel week available for allocation was staggered approximately 12 days after the interviewer was scheduled to start doorstep recruitment, to allow enough time to contact addresses and conduct placement interviews prior to the travel weeks starting.

Additionally, interviewers were once again only required to make one mid-week call – in contrast to telephone interviewing, the focus of these mid-week calls (ideally conducted F2F wherever possible) returned to the checking the diaries that the respondents were filling in, rather than populating the diaries on their behalf.

While F2F was intended as the primary approach, interviewers could also offer a telephone interview as back-up in cases where COVID-19 was a concern – this fallback approach was known as the phone back-up (PB). To ensure F2F was prioritised, the offer of a telephone interview could only be made if:

• respondents clearly stated they did not want interviewers to enter their home due to reasons related to COVID-19 (for example, shielding, fear of infection)
• the household failed the interviewer’s COVID-19 risk assessment
• the household was not willing to complete the interview F2F (used as a last resort only)

The PB process (once recruitment had been secured) was similar to the K2N process, aside from the fact that PB followed the same ‘fixed travel weeks’ approach as F2F.

The CAPI questionnaires were designed and implemented using the software system Blaise. A single Blaise instrument was used for the household, individual, vehicle and administrative sections of the questionnaire. Since the CAPI program had changed so little to accommodate telephone interviewing in response to the pandemic, the same program was used once F2F was reintroduced.

A separate Diary Entry System (DES) was written in Visual Basic. Selected CAPI variables were extracted and loaded into the NatCen field management system from where they were referenced by the DES. This process provides contextual information from the CAPI interview for those people inputting and editing travel diary data.

4.1.1 Interviewer start dates and assignments

Prior to 2014, interviewers began fieldwork (doorstep recruitment) at the start of each calendar month. However, analysis using 2012 data showed that this design led to an uneven spread of travel week start dates across the month due to interviewers following similar fieldwork patterns. In 2014 a new design was implemented to address this issue, whereby interviewers were assigned to start fieldwork on different dates to ensure that the interviewing dates were evenly spread across the month. The same principle applies to the travel week start dates, although the even spread of the travel week start dates has been further underpinned by the fixed travel week allocation method.

Until 2016 interviewer assignments were distributed evenly across the year, with the same number of assignments each month. However, this approach meant that certain months, particularly February, were over-represented in the data. As such, in 2016 a small refinement was made so that interviewer assignments were allocated evenly across a quarter, rather than by month. When allocating assignments to quota months it is done in such a way a naturally representative sample is distributed for each quarter. This same start date allocation process was used in the 2022 survey for points issued as K2N and F2F (this was not possible for P2T). In addition, the same allocation of assignments per quarter was used in 2022 as outlined above.

4.2 Interviewer briefings

In 2022 there were two types of briefings. New interviewers were briefed by NatCen’s research team during a series of two-day briefings. The briefings covered all aspects of the survey, including how to carry out the survey using either methodology (K2N and F2F or PB). The sessions included the completion of a dummy interview on interviewer laptops, as well as role-play exercises to practise doorstep technique and the placing and picking up of the travel diaries. Interviewers were also given a pre-briefing exercise. This involved completing their own travel diary using their own journey details for a week, studying the definitions manual and completing a short test on the NTS process.

Interviewers who had completed an NTS assignment over the previous 12 months attended a half-day refresher briefing shortly before the start of the survey year, to be trained on any changes that were new for the 2022 survey, including the reintroduction of the F2F methodology and fixed travel weeks allocation method.

In 2022 all briefings were conducted remotely via Microsoft Teams to ensure they were COVID-19 safe and that any travel restrictions were being adhered to.

4.3 Questionnaire and document despatch to interviewers

For K2N and F2F assignments the Operations Department made the sampled addresses and the questionnaire available to the interviewers for collection via a secure broadband connection before the start of each quota month. The relevant NTS materials were despatched to the interviewers by post. For P2T, after the cases had opted-in and they were re-grouped into new points (assignments), the Operations Department made the addresses available for interviewers to collect.

Any queries about transmission or other technical matters were dealt with by a helpline run from the Operations Department during working hours, and by a team of experienced interviewers working from home outside of working hours. Laptop maintenance was handled by a separate department within NatCen. The interviewers were also able to contact staff within the Operations Department who deal with the administration of fieldwork.

4.4 Contacting respondents

Knock-to-nudge methodology

For the K2N cases, interviewers were given advance letters to send to the selected addresses in advance of their first call (see Appendix B). The advance letter gave some general background to the survey and explained its importance, some of its uses, and how the household had been selected. It also stated that each respondent would receive a shopping voucher if all household members completed the survey. See section 4.13 for more details on the shopping voucher for respondents.

The letters included a space for interviewers to write in their name so that respondents knew who would be calling and to make the letters more personal. The letters were sent in ‘On Her Majesty’s Service’ envelopes and, as has been the case since June 2004 onwards, a book of first-class stamps was included with the advance letter as a gesture of goodwill to encourage respondents to take part.

In 2018 an experiment was run on a redesign of the advance letter. The advance letters on the NTS from 2019 onwards have reflected the redesigned letter developed in 2018.

Interviewers were notified of any refusals made to the Operations Department as a result of the advance letter. Interviewers were not required to visit these addresses and they did not count against interviewers’ individual response rates. However, they were classified as non-response (office refusals) in calculating the overall response to the survey.

A few days after the advance letters had been sent, interviewers contacted respondents by personal visit. Interviewers were required to make a minimum of 6 calls (visits) and to make sure that the days and times of the calls varied to maximise the chance of making contact with the selected household. If there was still no contact, only then could an interviewer return a case as a ‘non-contact’. Interviewers were also given a non-contact letter (which has been in place since November 2008) to post through the door of addresses where contact could not be made after 5 or 6 attempts (see Appendix C).

For the K2N methodology, interviewers were instructed to leave specific materials with participating households to help the interview proceed smoothly over the telephone. These materials included: a memory jogger (per individual), a set of showcards, a survey leaflet, and a milage chart (per vehicle).

The survey leaflet (see Appendix D) contained information about the reasons for carrying out the survey, how households were chosen and selected findings from previous surveys. The memory jogger (see Appendix F) was left with each respondent as an aide for them to record their travel. As respondents did not complete their diaries themselves, the jogger was intended to be a quick way for respondents to keep notes of the journeys they made and recall the information when speaking to the interviewer. To help the interview procced as smoothly as possible, interviewers were asked to leave showcards (see Appendix J) with respondents as some of the questions include a long list of answer options. Finally, interviewers were asked to leave the mileage chart (see Appendix G) with responding households (one per vehicle) to ensure that they were able to record their vehicle mileage as accurately as possible. However, knowing that these materials may increase the likelihood of some potential respondents refusing to take part in the survey, interviewers were briefed that the NTS process could be completed without leaving these materials.

Interviewers were also given access to the DfT Statistical Release Summary so that, when necessary, they could demonstrate to respondents the type of data collected by the NTS. This was intended to help boost response and make the survey easier to sell on the doorstep.

Face-to-face methodology (with phone back-up)

When F2F fieldwork was reintroduced from quarter two onwards many of the arrangements from K2N fieldwork remained in place, primarily because these arrangements resembled those that were already in place before the pandemic. This meant that F2F employed the same recruitment approach as K2N with respect to advance letters (and non-contact letter) and the requirements for minimum number of calls and the call pattern.

F2F differed from K2N in that it was not necessary to leave fieldwork documents such as showcards, mileage charts and memory joggers.

Push-to-Telephone methodology

For cases where interviewers were not available and a point could not be covered, the case was pushed to telephone (P2T). For these P2T cases, the contact approach was different in that there was no in-person contact between interviewers and potential respondents.

The advance letter was sent out by the NatCen Operations Department initially (see Appendix H). This letter varied slightly from the K2N advance letter in its wording, it also included a freephone number and online portal link for respondents to enable them to provide their contact details. The letter also stated that the incentive for a fully productive household was a £20 shopping voucher per household. The incentive for P2T was designed to maximise response to the P2T approach, as response to an opt-in approach is typically much lower than an interviewer led approach. This contrasted with the K2N approach where each respondent from a fully productive household would receive their own £5 shopping voucher.

In addition to this, a reminder letter was sent out to help ensure that the opt in rate was as high as possible (see Appendix I).

After opting in, a household was contacted by an interviewer over the phone to book an appointment to complete the placement interview.

4.5 Confidentiality

Respondents were informed in the advance letter that their participation was voluntary and that any information they provided would remain confidential and would not be passed on to anyone outside NatCen or the statistics section at DfT in a form that could be used to identify them. Respondents were provided with a telephone number and an email address for NatCen’s Operations Department that they could contact if they had any queries. Any substantive queries or complaints were subsequently passed on to researchers to deal with.

4.6 Allocation of Travel Weeks

The allocation of travel weeks varied in 2022 depending on the mode of completion (K2N, F2F, PB, or P2T). Traditionally on the NTS, interviewers were given fixed travel weeks, which were allocated to households when they reached a definitive outcome. To achieve this, each quota month is assigned a non-overlapping sequence of 30 to 31 travel week start dates. Individual interviewers are given a bespoke list (the “Travel Week Allocation Card”) of 17 travel week start dates, each of which is selected at random in such a way as to ensure that across all the interviewers working on a particular quota month an equal number of travel weeks will begin on each day in that month’s sequence. This means that it was possible to capture not only variations in travel behaviour within a month, but also differences across days of the week.

Because the number of trips respondents record often falls away as their travel week goes on, it is ensured that an approximately equal number of travel weeks begin on each of the seven days of the week. If, for example, all travel weeks were to start on Mondays, results would be biased toward travel behaviour on Mondays, Tuesdays and Wednesdays and under-represented travel on Saturdays and Sundays.

Interviewers are instructed to assign the first travel week in their list to the first address at which they reach a definitive outcome, whatever that outcome might be (including deadwood or refusal). They then assign the next travel week to the second address at which they reach a definitive outcome, and so on. Assigning travel weeks to non-participating addresses is the best way to ensure the travel records of the participating households cover the entire survey period evenly.

In 2022 the traditional fixed travel week approach was used for F2F and PB cases and was the dominant approach used from quarter two onwards (with the exception of P2T cases which used the rolling travel week as outlined below).

In 2021, in response to the COVID-19 pandemic, the travel week allocation process was amended. To offset the risk of drop-out between the telephone interview and the start of the travel week, both K2N and P2T moved to a rolling travel week. This meant that the travel week started the day before the placement interview.

As is the case under the face-to-face approach, the travel diary was introduced to respondents at the end of the placement interview. However, under the rolling travel week approach, Day 1 of the diary always starts the day before the interview. As such, Day 1 was completed on the same day as the placement interview with the interviewer entering the information on the paper diary on behalf of the respondent. It was also at this point that the interviewers would remind respondents about the mileage chart (see Appendix G), ensuring that respondents were clear on how to fill this out accurately.

In 2022 the rolling travel week approach was used for K2N and P2T cases and was primarily used in quarter one.

Section 1.4.1 outlines the effect of the different methodologies for allocating travel weeks on the data.

4.7 The placement interview

The interview was the same for K2N, F2F, PB and P2T cases. The first stage of interviewing consisted of the placement interview. This was conducted with all household members and consisted of three sections.

The household questionnaire was asked of the Household Reference Person (HRP), which is the householder with the highest income, or their spouse or partner. In exceptional cases the household questionnaire can be asked of another responsible adult aged 16 or over.

The individual questionnaire was asked of each household member, including children (although proxy information was collected for children under 11). A maximum of 10 people could be included. On the extremely rare occasions when interviewers encountered a household with more than 10 members, they were instructed to select the oldest 10 to take part in the interview, and to ensure that all vehicle owners were included.

The vehicle questionnaire was asked of the main driver for each vehicle in the household. A maximum of 10 vehicles could be recorded.

The proxy rules were relaxed to allow the telephone interviewing to function as easily as possible for K2N, PB and P2T cases. The interview allowed the HRP, or at least a person who can answer the questions on behalf of the household, to act as a proxy for the other individuals in the household if required. These proxy rules were more stringent for previous years of the NTS, when the primary data collection mode was face-to-face and were reintroduced in 2022 for all F2F cases.

The percentage of individuals who were interviewed in-person or by proxy in 2022 for the placement interview (as well as those not interviewed) is shown in Table 4.1. The table is broken down by age into the two main age groups: those aged under 16 (defined as a ‘young person’) and those aged 16 or over (defined as an ‘adult’). Comparable figures for 2021, 2020 and 2019 are shown in Tables 4.2, 4.3 and 4.4.

As expected, Table 4.1 shows that the vast majority of individuals aged under 16 were interviewed by proxy in 2022 (89%), which is comparable to the proportion interviewed by proxy in 2019 before the pandemic (85%) as shown in Table 4.4. Likewise, the figures shows that a high proportion of the individuals aged 16 or over were interviewed in-person in 2022 (67%), which is similar to the proportion interviewed in-person in 2019 (70%).

Note: figures in the tables may not total 100% due to rounding

Table 4.1: Method of individual interview at placement, by age (2022)

Method of interview	Aged under 16 (young person)	Aged 16 or over (adult)	Total
In-person	10%	67%	57%
Proxy	89%	32%	42%
Not interviewed	2%	1%	1%
Base (individuals)	1,685	8,182	9,867

Table 4.2: Method of individual interview at placement, by age (2021)

Method of interview	Aged under 16 (young person)	Aged 16 or over (adult)	Total
In-person	6%	60%	50%
Proxy	94%	40%	49%
Not interviewed	0%	0%	0%
Base (individuals)	1,949	9,061	11,010

Table 4.3: Method of individual interview at placement, by age (2020)

Method of interview	Aged under 16 (young person)	Aged 16 or over (adult)	Total
In-person	10%	64%	55%
Proxy	89%	36%	45%
Not interviewed	1%	0%	0%
Base (individuals)	1,129	5,715	6,844

Table 4.4: Method of individual interview at placement, by age (2019)

Method of interview	Aged under 16 (young person)	Aged 16 or over (adult)	Total
In-person	15%	70%	59%
Proxy	85%	30%	41%
Not interviewed	0%	0%	0%
Base (individuals)	3,163	12,920	16,083

Before 2020 and the onset of the COVID-19 pandemic, in the majority of cases, the placement interview took place before the start of the travel week. However, following the change to the travel week approach outlined in section 4.6, for 2020 and 2021 most placement interviewers took place on the second day of the travel week (with the start of the travel week being the day prior to the placement interview). From quarter two onwards when the fixed week travel week approach was reintroduced more cases had the placement interview before the start of the travel week.

4.7.1 The 2022 NTS questionnaire

Each section of the placement interview covered a number of different topics:

The household questionnaire included:

• the household grid
• questions about home deliveries and food shopping
• questions about children’s travel to school
• the household vehicles grid

The individual questionnaire included questions about:

• disabilities that affect travel
• methods of transport used
• walking
• cycling
• e-scooter
• driving licences
• internet use
• self-completion – satisfaction with transport services
• education, paid work and journey planning
• last paid job
• income
• location of work
• travel to work
• working at home
• ease or difficulty of travelling to work
• transport difficulties
• road accidents involving adults
• road accidents involving children
• special tickets or passes
• long-distance journeys
• permission for re-contact for follow up

The vehicle questionnaire included questions about:

• the vehicale registration number
• vehicle details
• parking
• mileage

Changes in 2022

The changes made to the NTS questionnaire in 2022 included:

• minor changes to the headings in the ethnic group question
• the addition of a question asking about the respondent’s religion
• minor changes to the sources of income show card
• minor changes to the frequency of attending employer’s premises question to reflect changes to working patterns as a result of the pandemic
• changing any references to ‘bicycle’ to ‘pedal cycle’
• changing any references to ‘disability’ to ‘health condition or illness’
• additional guidance for respondents completing the self-complete section including instructions for answering ‘don’t know’ or ‘prefer not to say’ as well as clarification for how the questions about loneliness are used
• the deletion of the question about mode preference for travel diary completion
• the addition of a question confirming whether the interview was completed in-person or over the phone

The coding of Standard Occupational Classification was carried out in 2022 according to the 2020 system (rather than 2010 which was the case previously).

All changes to the questionnaire for 2022 are shown in Appendix A2, and details of new method of travel modes are outlined in section 5.11.

Rotated questions

From 2002, some questions were designated to be ‘rotated’, such that they would be asked every other year. However, in 2006 questions on the frequency of use of bicycles, local bus and domestic air, which had previously been ‘odd year’ modular questions, were introduced on a permanent basis. In addition, a small number of ‘even year’ modular questions were deleted (questions on pavement conditions, cycle lane provision, availability of combined bus and rail ticket and whether vehicles had been driven in Northern Ireland in the last 12 months).

For the 2009 survey, the questionnaire was reviewed by DfT and NatCen. This resulted in further changes to the rotated questions and the introduction of sub-sample questions. The previously rotated questions on frequency of use of certain modes of transport, accessibility of services, reliability and frequency of trains and buses were introduced on a permanent basis – with some being asked of a sub-group of the sample only. From 2009, all households were randomly assigned to two sub-groups. One group were asked about attitudes to local services and the other were asked about accessibility of services. In 2013 the questions in sub-sample B covering accessibility of local services were removed. It was agreed that the sub-sample A questions on attitudes to local transport would be asked of the full NTS sample.

In 2017, attitudinal questions on satisfaction with transport services were asked of one member of the household aged over 16, administered by Computer Assisted Self-Interviewing (CASI). This member was randomly selected by the Computer Assisted Personal Interviewing program among the adults of the household present during the interview (proxy respondents could not be selected). The respondent completed the section on their own, using the interviewer’s laptop. See section 3.6 for more details on how this selection was made.

In 2020, in order to help reduce the questionnaire length, more questions were added to the rotation and some questions were removed with the intention of revisiting them every four years should there be policy-interest.

For 2022, the biennial rotating questions in Module A (even years questions) were asked, and the questions in Module B (odd years questions, last asked in 2021) were taken out.

Module A (even years) included questions about:

• cycling: barriers to cycling; and what would encourage more cycling
• driving licenses: reasons for not driving currently among those with a licence; reasons for no longer holding a licence; and age last drove
• ease or difficulty of travelling to work: difficulties with travelling to or from work by car, van, motorbike, scooter, or moped or by public transport; how easy is it to make journey to work, not using a car, van, motorbike, scooter, or moped; and what method of transport would they use instead
• transport difficulties: type of transport respondent has difficulty with; difficulties when travelling to the doctor’s surgery or hospital; difficulties experienced when visiting friends or relatives or other social activities; difficulties experienced when taking children to school or university; and difficulties experienced when travelling for other purposes
• parking: location of parking for vehicles
• mileage: purpose and miles driven outside of Great Britain

For reference, Module B (odd years) included questions about:

• home deliveries and food shopping: items that have been delivered and how often; and usual method of food shopping
• children’s travel to school: barriers of children walking to school more and what would encourage more walking to school more; and reasons for traveling to and from school with an adult
• disabilities that affect travel: use of powered or manual wheelchair and how often it is used; whether a respondent is a carer and time spent caring; and prevalence of special transport services and usage of any of these special services
• walking: barriers to walking more and what would encourage more walking in local areas
• driving licenses: reasons for not driving among those without a provisional licence; and likelihood to learn to drive
• travel to work: types of road used to travel to work; are respondents the driver or passenger travelling to work and how often is a lift given or received; and place of parking when driving to work
• working from home: days of the week normally working from home; and extent to which it is possible to work from home and how much can be completed from home

4.7.2 Harmonised questions

A number of harmonised questions are used in the NTS to allow users of the data to compare NTS data with those from other social surveys. These questions are listed in Table 4.5.

Table 4.5: Harmonised questions used in the 2022 NTS

Harmonised question	NTS question name	Year introduced
Sex	Sex	1998
Age	AgeIf	1998
Date of birth	Birth	2000
Marital status	MaritalStat	2013, with answer categories amended in 2013
Living arrangements	LiveWithN	2013
Ownership of accommodation	Hhldr	2002, with answer categories amended in 2003
Joint ownership	HiHNum	2002
Ethnic group	EthGroup	2001, with answer categories amended in 2011 and headings for answer categories amended in 2022
Length of residence	HLongA	1998
Relationship to head of household	RelHoH	1998 (question now asked as relationships of household members)
Relationships of household members	Relation	2013, with answer categories amended in 2013
Religion	Religion	2022
Accommodation type	Accom	2000
House type	HseType	2000
Flat type	FltTypN	2000
Other accommodation	AccOth	2000
Housing tenure	Ten1	1998, with answer categories amended in 2013
Car ownership	UseVcl	1998, with answer categories amended in 2003 and question text amended in 2004
Vehicle type	TypeVcl2	1998, with answer categories amended in 2003 (question was deleted in 2004, and has since been imputed using TypeVcl2)
Company car	PrivVcl	1998, with question text amended in 2009
General health	GenHeal	2017
Length of residence	HLongInd	2017
In employment	Wrking	1998
Training scheme	SchemeET	1998
Away from work	JbAway	1998
Own business	OwnBus	1998
Relative business	RelBus	1998
Looking for work	Looked	1998
Starting work	StartJ	1998
Inactive	YinAct	1998
Industry	IndD	1998
Job title	OccT	1998
Job description	OccD	1998
Job status	Stat	1998
Paid employment	EverWk	1998
Date of leaving last job	DtJbl	1998
Supervising employees	SVise	2001
Organisation size	EmpNo	1998
Self-employed	Solo	1998
Number of employees	SENo	1998, with answer categories amended in 2003
Full or part time work	FtPtWk	1998
Long-term unemployed	HowLong	2004
Educational qualifications	EdAttn1	2005
Professional or vocational qualifications	EdAttn2	2005
Highest qualification	EdAttn4	2005
Internet access	OnlineN	2013, with answer categories amended in 2013
Well-being	LackComp	2019
Well-being	LeftOut	2019
Well-being	Isolated	2019
Well-being	Lonely	2019
Disabilities that affect travel	Heallll	2018
Disabilities that affect travel	ImpCat1 to ImpCat10	2018
Disabilities that affect travel	LimitAct	2018

4.7.3 Placing the travel diary and other documents

For F2F cases in 2022 the approach for placing the travel diary and other documents followed the traditional NTS pre-pandemic approach. This approach involved the interviewer introducing and placing documents at the end of the placement interview. The seven-day travel diaries (see Appendix E) were placed for each household member, and the mileage charts (see Appendix G) were placed for each household vehicle.

For K2N, PB and P2T the interviewer completed the seven-day travel diary with the respondent, collecting the information from them over the phone and populating the paper version on behalf of the respondent. Interviewers were briefed to leave the mileage charts on the doorstep with the respondents where possible, in the case of K2N and PB interviews, and so would remind respondents that they should complete the mileage chart. In addition to the mileage charts, interviewers were briefed to leave memory joggers on the doorstep with respondents. Memory joggers are simplified pocket size diaries (see Appendix F), into which respondents could briefly note down their journeys.

The seven-day travel diary

Everyone in the household was eligible to complete a seven-day travel diary (completed by the respondent themselves, by proxy or by the interviewer depending on the methodology used for the interview) in which their travel activity was recorded. There are two versions, one for adults (respondents aged 16 and over) and one for children (the young person’s travel diary, aged 15 or younger).

Each trip was recorded, and details of origin and destination, purpose, mode, distance travelled, time, number travelling in their party, vehicles used, tickets used and cost was collected. In addition, the adult version of the travel diary collected details about of any parking costs as well as indicating whether they were a passenger or driver.

For F2F cases interviewers explained to respondents in detail how to complete the travel diary. They generally did this by entering the details of some typical journeys made by the respondent in the blank pages provided, often using the respondent’s previous day’s journeys. Some interviewers used the NTS definitions manual to help describe the level and type of details required.

Note: All survey definitions are given in the NTS definitions manual, copies of which are available on request.

Since 2014 interviewers have been also provided with a list of key points to cover when placing and checking a travel diary. Simplified pocket size diaries or memory joggers (see Appendix F), into which respondents could briefly note down their journeys, were placed with respondents if the interviewer felt they would be helpful.

For K2N, PB and P2T cases, interviewers collected information from respondents via telephone to populate the travel diaries. Interviewers were briefed to provide respondents with a memory jogger in K2N and PB cases if possible. In addition, interviewers were able to make use of the NTS definitions manual and the list of key points to cover when placing and checking a travel diary when they were populating the diaries on behalf of respondents.

The travel diary was redesigned in 2007 following an extensive development study. Full details of this study are available on the Department for Transport’s website. For further detail see McGee A, Gray M & Collins D (2006), NTS Travel Record Review Stage 1; and McGee A, Gray M, Andrews F, Legard R, Wood N and Collins D (2006) NTS Travel Record Review Stage 2.

From September to December 2008, a slightly different design of travel diary was trialled with half of the sample. The revised travel diary had rows for seven journeys on days 1 to 6, rather than six, and slightly revised text to remind respondents to include short trips and short walks on day 7. This was done to examine the effect of these changes on trip reporting, following changes being observed in the diary data between 2006 and 2007. No significant effects were detected. From 2009 the revised travel diary was used.

The travel diary underwent a further small redesign in 2013, with the removal of the column for recording the cost of road tolls or congestion charges where applicable, and the removal of the column for recording the share of any taxi costs. In 2014 a note was added to the top of the recording pages for Day 1 and Day 7 to remind respondents to complete the mileage chart.

In 2016, two versions of the diary were trialled, one in which respondents were asked to record their short trips (under 1 mile) on day one and one in which respondents were asked to record their short trips on day seven. As this experiment showed that recording was more accurate on day one than on day seven, in 2017 only one version of the diary was used with short walk recording on day one. A full list of changes that have been made to the travel diary since 2002 can be found in Appendix A4.

For 2022, the travel diaries collected information on:

• purpose of journey
• time left
• time arrived
• origin: where the journey started (from village, town or local area)
• destination: where the journey ended (to village, town or local area)
• method of travel (car, bus, walking etc.)
• distance (in miles)
• time travelling (in minutes)
• number of people in party travelling
• which car or motorcycle etc. was used (if journey was made by private transport)
• ticket type: single, return or travel card etc. (if journey was made by public transport)
• cost (if journey was made by public transport)
• number of boardings: the number of trains or buses etc. used to reach journey destination (if journey was made by public transport)

On Day 1 of the travel week, information was collected on all walks over 50 yards. However, on Days 2 to 7, only walks that were one mile or more were recorded (approximately equivalent to taking 20 minutes or more).

Additionally, the adult travel diaries (for those aged 16 or over) collected information on:

• whether the respondent was the driver or the passenger (if journey was made by private transport)
• how much was paid for parking (if journey was made by car or motorcycle etc.)

The young person’s travel diaries (for those aged under 16) also collected additional information on the number of people in party travelling, by splitting out the party into the number of adults and the number of children (whereas in the adult travel diaries only the total number of people was recorded).

Long-distance journeys

The NTS also collects details about any long-distance journeys, defined as trips of 50 miles or more made within Great Britain. In 2006, the period for which respondents were asked about long-distance journeys was changed from three weeks to one week (in addition to the travel week). This change was made to decrease the burden on respondents and increase the reliability of the data. Until 2015, a long-distance journey card was left behind to be filled in by respondents, and which was collected at the pick-up interview. Removing the need to leave this card behind means that the data can be entered straight into the CAPI, and so allowing potential queries to be resolved when respondents are actually present.

The week for which respondents were asked about long-distance journeys was normally the seven days preceding the placement interview. In cases where the placement interview was conducted part way through the travel week, the seven days were instead taken to be the week preceding the start of the travel week.

Long-distance journeys that took place during the travel week were covered in the travel diary. In total, a maximum of 40 long-distance journeys could be recorded during the interview.

The mileage chart

In addition to the diaries, for F2F cases, a mileage chart was placed at the end of the placement interview for each household vehicle. The driver was encouraged to keep this chart in their vehicle. The chart required the driver to record the milometer reading at the start and end of the travel week.

For K2N and PB cases the mileage chart was provided to respondents as part of the doorstep recruitment stage as the interviewer would not be able to place it in person at the end of the placement interview (as this was conducted via telephone).

As the interviewers did not contact respondents in-person for P2T cases the mileage chart was not issued to respondents. Data was instead collected over the phone, based on the respondent’s knowledge of their mileage.

Due to the change in approach required for the placement of the mileage chart for K2N, PB and P2T cases some caution should be used when analysing this data. For example, as the travel week started the day before the placement interview for K2N and P2T cases it is likely that the initial mileage chart reading would be an estimate (unless no mileage was used on day one of the travel week). Also, respondents could lose the mileage chart between receiving it on the doorstep and the start of the travel week or could refuse to accept it.

See Appendix G for a copy of the mileage chart.

4.7.4 Length of the placement call

The average length of the placement call (that is, the placement interview plus the time taken to explain and complete the first days of the diary) was 52 minutes in 2022, and varied according to household size, as shown in Table 4.6. Comparable figures for 2021, 2020 and 2019 are shown in Tables 4.7, 4.8 and 4.9.

As expected, Table 4.6 shows that the mean length of the placement call in 2022 tended to be longer for larger households, although the increase in time for each additional household member was not linear. For example, the mean length for a single-person household was 40.37 minutes, and then 54.46 minutes for a two-person household and 56.51 minutes for a three-person household. The longest mean time was 83.89 minutes for households with eight people.

The 2022 figures are similar in some regards to those shown in Table 4.9 from before the pandemic in 2019. For example, the mean length in 2019 was 40.41 minutes for single-person households and 54.77 minutes for two-person households, very close to the mean lengths in 2022. However, three-person households had a longer mean length of 60.69 minutes in 2019. Overall, the mean length was longer in 2019 than in 2022 for households of three to six people. By contrast, the mean length was shorter in 2019 than in 2022 for households of seven or more people, although this is based on a very small number of households who had seven or more people.

Table 4.6: Mean length of placement call (in minutes), by household size (2022)

Number of people in household	Mean length (minutes)	Base
1	40.37	1,305
2	54.46	1,704
3	56.51	602
4	61.93	548
5	61.64	142
6	76.9	51
7	76.78	9
8	86.89	9
9	63	1
10	-	-
All households	52.08	4,371

Table 4.7: Mean length of placement call (in minutes), by household size (2021)

Number of people in household	Mean length (minutes)	Base
1	37.34	1,381
2	52.09	1,864
3	56.03	722
4	61.46	617
5	67.20	176
6	61.85	40
7	83.00	11
8	88.17	6
9	61.00	3
10	-	-
All households	50.41	4,820

Table 4.8: Mean length of placement call (in minutes), by household size (2020)

Number of people in household	Mean length (minutes)	Base
1	35.58	923
2	47.07	1,242
3	53.46	384
4	57.63	342
5	65.57	119
6	65.97	30
7	57.86	14
8	125.00	3
9	-	-
10	96.00	2
All households	46.65	3,059

Table 4.9: Mean length of placement call (in minutes), by household size (2019)

Number of people in household	Mean length (minutes)	Base
1	40.41	1,879
2	54.77	2,522
3	60.69	968
4	64.04	958
5	65.23	273
6	69.08	79
7	71.79	24
8	69.50	6
9	80.20	5
10	89.33	3
All households	53.63	6,717

4.8 The reminder call

Historically on the NTS, once the travel diary had been placed, the next stage was to remind the household to start recording their journeys on the date allocated to them (as the travel week was allocated and could be set in the future). Interviewers did this either by sending a reminder card, or by making a reminder phone call one or two days before the start of the travel week. Reminder calls were reintroduced for F2F and PB cases from quarter two onwards in 2022.

For K2N and P2T cases reminder calls were not used in 2022 continuing with the same approach as 2021. The reminders were intended to remind respondents of the beginning of their travel weeks, however, as K2N and P2T cases used rolling travel weeks, and so started their placement interview on the second day of the travel week, the reminders were not necessary for this approach.

4.9 The mid-week check call

For F2F cases, interviewers were encouraged to conduct a call halfway through the travel week, to encourage and help respondents with any difficulties they might be having filling out their travel diaries. This could be either a phone call or a personal visit and was at the interviewer’s discretion, although they were strongly encouraged to conduct an in-person check for elderly participants.

For PB, K2N and P2T cases the mid-week check call was used by interviewers to complete several more days of the travel diaries on the respondent’s behalf. This call was always completed over the phone. The intention of this call was to help ensure that the data quality on the travel records remained as high as possible, by minimising the number of days between the respondent travelling and then having to recall their travel to the interviewer over the phone.

For PB cases, a second mid-week check call was strongly recommended to interviewers if the travel week occurred after the day of the interview (as was possible with the ‘fixed travel week’ approach to allocating the travel weeks for PB cases). Ideally this was conducted with the first mid-week call taking place on Day 2 of the travel week and the second mid-week check on either Day 4 or 5. For K2N and P2T cases this second call was not necessary, due to the ‘rolling travel week’ approach to allocating travel weeks, which meant the travel week started the day before the interview, and so the interviewer could collect information about the first two days of the travel week at the end placement interview.

The proportion of households receiving a mid-week check in 2022 (and the proportion conducted either by phone or in-person) is shown in Table 4.10. Comparable figures for 2021, 2020 and 2019 are shown in Tables 4.11, 4.12 and 4.13.

In 2022, 74% of fully productive households had a mid-week check (either by phone or in-person), which is higher than the years heavily impacted by the pandemic (2020 and 2021), and closer to 2019 (80%). By contrast, the number of in-person mid-week checks was 18% in 2022 and 30% in 2019 (for fully productive households), which is mostly likely to be explained by the use of PB, K2N and P2T in 2022 (because in such cases only a mid-week check by phone could have been conducted).

Note: figures in the tables below may not total 100% due to rounding

Table 4.10: Proportion of households where a mid-week check was conducted (either by phone or in-person), by fully and partially co-operating households (2022)

Type of check	Fully co-operating	Partially co-operating	Total
Mid-week check conducted by phone	56%	40%	53%
Mid-week check conducted in-person	18%	11%	17%
No mid-week check	25%	47%	29%
Base (households)	3,646	723	4,369

Table 4.11: Proportion of households where a mid-week check was conducted (either by phone or in-person), by fully and partially co-operating households (2021)

Type of check	Fully co-operating	Partially co-operating	Total
Mid-week check conducted by phone	59%	43%	58%
Mid-week check conducted in-person	4%	4%	4%
No mid-week check	37%	53%	38%
Base (households)	4,429	390	4,819

Table 4.12: Proportion of households where a mid-week check was conducted (either by phone or in-person), by fully and partially co-operating households (2020)

Type of check	Fully co-operating	Partially co-operating	Total
Mid-week check conducted by phone	35%	39%	35%
Mid-week check conducted in-person	9%	9%	9%
No mid-week check	56%	51%	56%
Base (households)	2,822	237	3,059

Table 4.13: Proportion of households where a mid-week check was conducted (either by phone or in-person), by fully and partially co-operating households (2019)

Type of check	Fully co-operating	Partially co-operating	Total
Mid-week check conducted by phone	50%	33%	48%
Mid-week check conducted in-person	30%	22%	29%
No mid-week check	20%	44%	23%
Base (households)	6,162	663	6,825

4.10 The pick-up call

For F2F cases, at the end of the travel week, the interviewer called at the household (generally within a few days) to pick up and check the travel diaries and to carry out another much shorter interview, known as the pick-up interview. The pick-up interview collected information about:

• new vehicles acquired since the placement interview (for the household)
• the disposal of vehicles recorded at the placement interview (for the household)
• new driving licenses acquired since the placement interview (for individuals)
• new season tickets acquired since the placement interview (for individuals)
• mileage details (for each household vehicle)

This pick-up call was also where the diaries were picked-up and checked before being sent back for coding by NatCen’s Operation Teams.

For PB, K2N and P2B cases this pick-up interview was conducted over the phone (following the amended approach used in 2020 and 2021). Historically, as part of the face-to-face approach (outlined above), the pick-up call was also when the diaries were picked up and checked. However, for PB, K2N and PB cases, rather than picking up and checking the travel diaries, the remaining days of the travel record were completed by the interviewer over the phone (with the earlier days of the travel week having been completed after the placement interview and at the mid-week check).

At the pick-up interview for F2F cases, the mileage chart was collected, and the details transferred into the CAPI questionnaire either during the interview or later on by the interviewer at home.

For pick-up interviews conducted over the phone (K2N, PB and P2T), the data collected by the mileage chart was also collected over the phone at this point. Interviewers would ask the respondents to populate their mileage chart at the beginning of the travel week and then collect the information from the respondent during the pick-up interview.

Before 2013, if all household members had completed a travel diary and the placement questionnaire was complete, the household was issued with a promissory note which informed them of the number of £5 gift vouchers they would receive. These vouchers would then be sent to them by the Operations Department. Since 2013, respondents were instead given a gift card by interviewers during the pick-up call. Interviewers explained to respondents that the giftcard would be activated by the office within two working days. For K2N and PB cases in NTS 2022 the £5 incentive voucher was used again but this was sent out by NatCen’s Operation Department to ensure that there was no face-to-face contact between interviewers and respondents. For the P2T cases, a £20 incentive card was used and they were also sent out by NatCen’s Operation Team, rather than being issued by an interviewer.

Starting in 2019, interviewers also handed out a thank you letter at the pick-up interview (see Appendix K). The thank you letter was from the DfT and given as a recognition for the time and effort of respondents. It also offered respondents another chance to sign up to the National Travel Attitudes Study (NTAS) web panel. For F2F cases this followed the 2019 protocols in 2022 (that is, handed over at the pick-up interview). For K2N, PB and P2T this was mailed out by the Operations Team with the giftcard(s).

During face-to-face data collection, the pick-up interview could be done either on the laptop, or using a paper questionnaire which was transferred into the CAPI questionnaire by the interviewer afterwards or by the operations team when paperwork was returned to the office. A paper version of the pick-up questionnaire was introduced in 2002 to enable interviewers do the pick-up interview on the doorstep where respondents were unwilling to let them into the property again. For all K2N, PB and P2T cases the pick-up interview was completed using the CAPI questionnaire.

Table 4.14 shows the mean length (in minutes) of pick-up interviews for 2022 and all previous survey years going back to 2002. On average, the pick-up call (including the interview and checking the travel diaries) lasted about 15.5 minutes for fully productive households in 2022. This call was made within six days of the end of the travel week. The 2022 average length of the pick-up call was similar to the pre-pandemic figure (14.5 in 2019) due to the return to the traditional face-the-face methodology from quarter two onwards, with interviewers checking diaries rather than populating the remaining days of the diaries, as was the case during the pandemic.

The mean length of the pick-up interview reported here is calculated using the amount of time entered by the interviewer into the CAPI program. Although the length of pick-up is also calculated within the CAPI programme, this is not a reliable source because the pick-up interview is sometimes conducted on paper with the interviewer entering the information into the program at home. In previous technical reports, the pick-up length has not been calculated in a consistent manner. The pick-up interview lengths shown in Table 4.14 replace those in previous NTS technical reports and are based on the interviewer-reported length.

Table 4.14: Mean length (in minutes) of pick-up interview in minutes, by fully co-operating and total co-operating households (from 2022 going back to 2002)

Year	Fully co-operating	Total co-operating
2022	15.5	15.5
2021	18.1	18.0
2020	17.1	16.9
2019	14.5	14.4
2018	15.1	15.0
2017	14.7	14.6
2016	15.1	15.2
2015	15.5	15.3
2014	15.4	15.3
2013	15.1	15.0
2012	15.9	15.7
2011	16.4	16.3
2010	16.0	15.9
2009	16.4	16.2
2008	16.2	16.0
2007	16.6	16.4
2006	16.3	16.1
2005	18.6	18.5
2004	19.0	18.7
2003	18.6	16.3
2002	18.4	18.0

4.11 Gazetteer

A new placename gazetteer was introduced in 2007. The gazetteer is used to code the location of where respondents work and the origin and destination of any long-distance journeys during the CAPI interview. It is also used to code the location of journeys made in the travel record using the Diary Entry System. The new gazetteer holds a much more complete list of locations in Great Britain which is based on 1km grid references.

During the interview and the data checking stage, the CAPI and Diary Entry System uses the gazetteer’s grid references to calculate reasonably precise distances between each named location using checks based on straight line distances. For trips of 15 miles or over, respondents’ estimates of distance are flagged for checking if they are not between 0.75 and 1.75 as the crow fly miles at the data processing stage. Discrepancies in distance estimates are not flagged where respondent and crow fly miles are both below 15 miles.

Up to 2006, when the previous gazetteer was used, distance checks were based on minimum and maximum distances for a journey within a county or between any pair of counties. These checks were therefore less sensitive than the current checks.

4.12 Outcome coding

Interviewers were required to assign an outcome code to every address in their assignment for F2F, K2N and PB cases. For P2T cases, interviewers assigned outcomes to all cases that opted into the survey, with any addresses that did not opt in were assigned an outcome manually by NatCen’s programming team. The range of possible fieldwork outcomes is shown in Table 4.15.

The fully and partially co-operating codes (110 to 130 and 240 to 260) were automatically computed by the CAPI questionnaire. (These fieldwork outcome codes are different to the participation categories that are used for the purposes of weighting.) For a household to be classed as fully co-operating, the placement interview had to be fully completed and filled in travel diaries had to be collected for all household members. To be classed as fully completed, the placement interview needed the household section, all individual interviews (whether in person or by proxy), and at least one vehicle section (if applicable) to be completed. If some household members were interviewed but full travel diaries were not gained from everyone, the household was coded as partially co-operating.

Table 4.15: NTS outcome codes

Type	Outcome	Code
Fully co-operating	Fully productive: All desired respondent(s) in person	110
Fully co-operating	Fully productive: Partly by desired respondent(s), partly by proxy	120
Fully co-operating	Fully productive: By proxy	130
Partially co-operating	Partial productive: Desired respondent(s)	240
Partially co-operating	Partial productive: Partly by desired respondent(s), partly by proxy	250
Partially co-operating	Partial productive: By proxy	260
Non-contact	No contact with anyone at address	310
Non-contact	Contact made at address, but not with member of selected household or a responsible adult	320
Non-contact	Household opt-in but telephone number wrong	333
Refusal	Office refusal	410
Refusal	Contact made but information refused about number of HHs or DUs	420
Refusal	Refusal at introduction or before interview, proxy refusal, or refusal due to COVID-19 and no agreement to remote interviewing	430
Refusal	Refusal during interview	440
Refusal	Broken appointment – no recontact	450
Other unproductive	Illness at home during survey period	510
Other unproductive	Absence from home or in hospital all survey period	520
Other unproductive	Physical or mental incapacity	530
Other unproductive	Language difficulties	540
Other unproductive	OFFICE APPROVAL ONLY - Lost productive	550
Other unproductive	Household member ill with COVID-19 or related symptoms or Household member shielding from COVID-19 or Household member has been instructed to self-isolate	560
Other unproductive	Interview completed but respondent requested deletion	591
Other unproductive	OFFICE APPROVAL ONLY - Other unproductive	599
Unknown eligibility	OFFICE APPROVAL ONLY - Not attempted	612
Unknown eligibility	Not attempted due to COVID-19 local lockdowns	614
Unknown eligibility	OFFICE APPROVAL ONLY – Inaccessible, or Inaccessible due to COVID-19	620
Unknown eligibility	OFFICE APPROVAL ONLY - Unable to locate address	630
Unknown eligibility	Unknown whether address contains residential housing – no contact made	640
Unknown eligibility	Residential address – unknown whether occupied by eligible household – no contact	650
Unknown eligibility	Other unknown eligibility	690
Unknown eligibility	P2T opt in letter sent but no response	699
Ineligible or deadwood	Not yet built or under construction	710
Ineligible or deadwood	Demolished or derelict	720
Ineligible or deadwood	Vacant or empty	730
Ineligible or deadwood	Non-residential address e.g. business, school, office factory etc.	740
Ineligible or deadwood	Address occupied, no resident household e.g. holiday or weekend home	750
Ineligible or deadwood	Communal Establishment or Institution (no private dwellings)	760
Ineligible or deadwood	Residential, but no eligible respondent (e.g. no-one aged 16 and over)	770
Ineligible or deadwood	OFFICE USE ONLY - Address out of sample	780
Ineligible or deadwood	Other ineligible	790
Ineligible or deadwood	Unknown whether address contains residential housing – info refused	810
Ineligible or deadwood	Contact made but not with someone who could confirm whether occupied or residential	820
Ineligible or deadwood	Residential address, unknown whether occupied by eligible hholds or persons – info refused	830
Ineligible or deadwood	Unable to confirm eligibility due to language difficulties	850
Ineligible or deadwood	Other unknown eligibility	890

The household was coded as partially co-operating if (any of the following):

• the household section of the placement questionnaire was not completed
• anyone was coded as ‘not available’ for the individual section
• no vehicle questionnaire sections were complete (if applicable)
• travel diaries were not collected for all household members at pick-up
• any of the travel diaries were incomplete (for example, missing days)

For 2021, in response to the COVID-19 pandemic, some new outcomes were added to the survey which were also used in 2022, namely:

• 433, refusal of F2F due to COVID-19 (no agreement to remote interviewing)
• 561, household member ill with COVID-19 or related symptoms
• 563, household member shielding from COVID-19
• 565, household member has been instructed to self-isolate
• 614, not attempted due to COVID-19 local lockdowns
• 621, inaccessible due to COVID-19

In 2020, two specific P2T outcome codes were added: 333 which was used for the small proportion of households that opted into the survey, but gave an incorrect phone number; and 699, which was used for households that did not opt in. As these households did not respond to the letter, very little was known about their eligibility to participate in the survey and as such they were given a separate unknown eligibility outcome.

Addresses which were not issued to an interviewer or which were issued but not visited were given an outcome code of 612.

4.13 The gift voucher incentive

In 2002 an experiment to test the effect of offering incentives to NTS sample members was conducted from the beginning of the July 2002 quota until the end of the December 2002 quota. This experiment found that offering an incentive did significantly increase the likelihood of gaining full household co-operation. At the end of 2002, it was decided that the incentive payment would be offered as a part of the NTS survey for 2003 onwards.

Note: For further information about the incentive experiment see section 3.12 in the 2002 NTS Technical report, and Stratford et al. (2003), Incentives experiment report, both available on request from DfT.

Interviewers gave each household a signed promissory note if all household members had completed the placement interview and completed a travel diary. These notes promised the delivery (by post) of £5 vouchers by the Operations Department. Interviewers then sent their copy of the promissory note to the Operations Department. On receipt of the signed promissory notes, the travel diaries were inspected, and high street vouchers were sent to the household if the documents met the specified criteria of completeness.

In 2009 an incentive experiment was conducted to review the impact of higher value incentives and different incentive structures on response, potential non-response bias and data quality. Two alternative incentives were tested: firstly unconditional £5 voucher with advance letter plus £10 voucher per person if the household is fully productive; secondly unconditional £5 voucher with advance letter plus £5 voucher after completion of CAPI interview, plus £5 voucher per person if the household is fully productive and finally the standard NTS incentive structure. Neither of the higher value incentive structures trialled in this experiment achieved a significantly higher response rate than the pre-existing incentive structure. There was also little difference between the incentive options in terms of the composition of the achieved sample or the quality of the data collected. In light of these findings, no changes to the incentives structure were recommended.

From 2013 onward, interviewers were given the task to check the completion of the diaries when they were coming back to the respondents’ home for the pick-up interview and to issue the vouchers themselves. Interviewers would issue a £5 voucher per fully completed diary only if all members of the household had filled their diary.

For 2022, all fully productive F2F, K2N and PB cases were issued with the same £5 voucher as they had been with the traditional F2F cases as highlighted above. However, for K2N and PB to ensure that interviewers did not make prolonged face-to-face contact with respondents and given that the pick-up interview was conducted over the phone, the incentives were issued by NatCen’s Operation Team.

For the P2T cases, the incentive structure was slightly different to help encourage respondents to participate in the survey. A book of stamps was not included alongside the advance letter and respondents were offered a £20 incentive for becoming a fully productive household. As with K2N and PB, the incentives were issued centrally by the NatCen Operations Team rather than being issued by interviewers.

4.14 Response rates

National and London response

Tables 4.16 to 4.19 show the response rates in 2022 for England as a whole (the national response rate), the response for Inner London and Outer London, and finally the response for the rest of England excluding London. The overall national response rate in 2022 was 31%, but this was lower in Inner London (18%), the same in Outer London (31%), and slightly higher in the rest of the country (32%).

Table 4.16: NTS National (England) response rates

Category	Achieved Sample	Achieved Sample Rate	Standard Response Rate
Set sample	12,852	100%	not applicable
Ineligible or deadwood	922	7%	not applicable
Unknown eligibility	2,499	19%	not applicable
Eligible households	11,707	91%	100%
Fully co-operating	3,646	28%	31%
Partially co-operating	723	6%	6%
Refusal to co-operate and other unproductive	4,105	32%	51%
Non-contact	957	7%	12%

Table 4.17: NTS Inner London response rates

Category	Achieved Sample	Achieved Sample Rate	Standard Response Rate
Set sample	918	100%	not applicable
Ineligible or deadwood	81	9%	not applicable
Unknown eligibility	269	29%	not applicable
Eligible households	803	88%	100%
Fully co-operating	143	16%	18%
Partially co-operating	44	5%	5%
Refusal to co-operate and other unproductive	305	33%	61%
Non-contact	76	8%	15%

Table 4.18 : NTS Outer London response rates

Category	Achieved Sample	Achieved Sample Rate	Standard Response Rate
Set sample	1,241	100%	not applicable
Ineligible or deadwood	105	8%	not applicable
Unknown eligibility	98	8%	not applicable
Eligible households	1,127	91%	100%
Fully co-operating	348	28%	31%
Partially co-operating	81	7%	7%
Refusal to co-operate and other unproductive	504	41%	51%
Non-contact	105	8%	11%

Table 4.19: NTS England excluding London response rates

Category	Achieved Sample	Achieved Sample Rate	Standard Response Rate
Set sample	10,693	100%	not applicable
Ineligible or deadwood	736	7%	not applicable
Unknown eligibility	2,132	20%	not applicable
Eligible households	9,774	91%	100%
Fully co-operating	3,155	30%	32%
Partially co-operating	598	6%	6%
Refusal to co-operate and other unproductive	3,296	31%	50%
Non-contact	776	7%	12%

As mentioned in section 3.4 the NTS oversamples Inner and Outer London with the aim of achieving responding sample sizes that reflect the regional distribution without the need for corrective weighting. The degree of oversampling in 2022 was based on estimates of differences in response rates between Inner London, Outer London and the rest of England.

From 2006 onwards, weights were introduced in order to correct for non-response (see Chapter 6 for a detailed description of the weighting). Data back to 1995 have been weighted retrospectively.

Response by data collection mode

The use of P2T methodology means that the standard response rate can be misleading. For P2T, addresses that did not opt-in to the study in response to the invitation letter were given an outcome code of 699, which is classified as ‘unknown eligibility’.

Given the relatively low opt-in rate for the P2T sample and the very low number of addresses that were identified as ineligible or deadwood, this resulted in an unknown eligibility rate that was significantly higher than the level seen before the pandemic using the traditional F2F data collection methodology. For the total sample including all methodologies (P2T, K2N, F2F and PB) the unknown eligibility rate was in 19% in 2022, compared to 1% in 2019. For the P2T sample, however, the rate was 91%.

Similarly, the overall rate of known ineligible or deadwood cases was significantly lower than pre-pandemic, with 7% of the total sample in 2021 compared to 11% in 2019. For the P2T sample only, however, the rate was close to zero (0%).

Consequently, the estimation of eligible addresses was affected. The estimated number of eligible households (as used in all Tables 4.16 to 4.22) is calculated by firstly deducting the ineligible or deadwood cases from the total sample, and then secondly deducting a proportion of the cases with unknown eligibility. The second deduction is made on the assumption that at least some of the addresses with unknown eligibility would have been ineligible or deadwood. The proportion used in this calculation is simply the inverse of the known eligibility rate.

The dual effect of higher rates of unknown eligibility and lower rates of ineligible or deadwood cases being identified on estimating the number of eligible addresses was minor for the total sample, but the impact on the P2T sample was considerable. As such, it is important to understand response rates by survey mode.

Firstly, the combined response rates for K2N and F2F oo PB are presented in Table 4.20, which show that the response for cases issued to an interviewer in 2022 was 35%.

Table 4.20: NTS response rates in 2022 for cases issued to an interviewer

Category	Achieved Sample	Achieved Sample Rate	Standard Response Rate
Set sample	11,186	100%	not applicable
Ineligible or deadwood	921	8%	not applicable
Unknown eligibility	980	9%	not applicable
Eligible households	10,177	91%	100%
Fully co-operating	3,528	32%	35%
Partially co-operating	719	6%	7%
Refusal to co-operate and other unproductive	4,085	37%	47%
Non-contact	953	9%	11%

Table 4.21 presents the response rate achieved for P2T cases (7%). However, as discussed above, this assumes that virtually all addresses are eligible, which is not the case with PAF samples.

In order to calculate the P2T response rate in a way which is comparable to the K2N and F2F/PB response rate, it is important to adjust for expected levels of ineligibility. Table 4.22 presents the P2T response rate when adjusted based on an ineligible or deadwood rate of 11% (that is, the rate identified in the 2019 face-to-face survey), resulting in a response of 9%.

Note: due to the high number of P2T cases with unknown eligibility, the Standard Response Rate figures (shown in the tables below) are substantially higher for ‘refusal to co-operate and other unproductive’ addresses and ‘non-contact’ addresses, as compared to cases issued to an interviewer.

Table 4.21: NTS Push-to-Telephone response rates

Category	Achieved Sample	Achieved Sample Rate	Standard Response Rate
Set sample	1,666	100%	not applicable
Ineligible or deadwood	1	0%	not applicable
Unknown eligibility	1,519	91%	not applicable
Eligible households	1,655	99%	100%
Fully co-operating	118	7%	7%
Partially co-operating	4	0%	0%
Refusal to co-operate and other unproductive	20	1%	77%
Non-contact	4	0%	15%

Table 4.22: NTS Push-to-Telephone response rates using the 2019 eligibility rate

Category	Achieved Sample	Achieved Sample Rate	Standard Response Rate
Set sample	1,666	100%	not applicable
Ineligible or deadwood	183	11%	not applicable
Unknown eligibility	1,337	80%	not applicable
Eligible households	1,336	80%	100%
Fully co-operating	118	7%	9%
Partially co-operating	4	0%	0%
Refusal to co-operate and other unproductive	20	1%	76%
Non-contact	4	0%	15%

4.15 Back-checking and quality control

Like all NatCen projects in the field, the NTS was back-checked to ensure that interviewers were working to the standards to which they were trained and in accordance with the specific project requirements on which they were briefed.

A minimum of 10% of the total productive interviews were back-checked, the majority (usually 90%) by telephone but where this was not possible (usually 10%) by letter. If the responses received indicated significant deviations from the standards set, a supervisor was asked to revisit the address(es) concerned personally. Back-checking was carried out usually within 2 weeks, and always within 4 weeks, of the interview date.

Chapter 1 – Fieldwork approach in 2022

Chapter 2 – Background

Chapter 3 – Sample Selection

Chapter 4 – Fieldwork Procedures and Response Rate

Chapter 5 – Data Processing

Chapter 6 – Weighting

Glossary

Appendices