Correspondence

National Child Measurement Programme: school feedback letter metadata 2023

Updated 9 October 2023

This information is intended for use by local authority public health teams. It explains the information contained within the National Child Measurement Programme (NCMP) school feedback letters.

Classification of overweight and obesity

For population monitoring purposes, a child’s body mass index (BMI) is classed as overweight or obese where it is on or above the 85th centile or 95th centile, respectively, based on the British 1990 growth reference (UK90) data.

The population monitoring cut-offs for overweight and obesity are lower than the clinical cut-offs (91st and 98th centiles for overweight and obesity) used to assess individual children. This is to capture children in the population in the clinical overweight or obesity BMI categories, and those who are at high risk of moving into the clinical overweight or clinical obesity categories. This helps ensure that adequate services are planned and delivered for the whole population.

NCMP data included in the school letters

Up to 3 years of data (from the 2018 to 2019, 2019 to 2020 and 2021 to 2022 collections) have been combined to create a large enough sample size to provide a reliable picture of the weight status of the school population, and minimise instances where the data needs to be suppressed to prevent individual children being identifiable.

In a small number of cases, data is not available for all 3 years, most likely due to measurements in schools being scheduled during April to July 2020 during the COVID-19 lockdown periods so the school was missed from the 2019 to 2020 data. Where only one or two years of data is included, this is noted on the relevant feedback letters.

Data from the 2020 to 2021 NCMP collection year has not been included in the school letters due to large gaps in the data collection because of the COVID-19 pandemic. Around 300,000 children (25% of previous full measurement years) were measured in 2020 to 2021. While it was possible to produce prevalence estimates at national and regional level, the sample size was not intended to enable the production of comprehensive and robust local authority or school-level data. Therefore, an additional year of NCMP data from 2018 to 2019 is included instead of 2020 to 2021 to ensure that large enough numbers are available for analysis.

Rounding of data

The percentage figures for prevalence of overweight and obesity have been rounded to the nearest whole number. A statement has been included in the footer of the letter stating that, due to rounding, figures for overweight and obesity in the text may not add up to exactly the same number shown in the chart.

Participation rates for reception and year 6

The England participation rates shown in the letter are for the 2018 to 2019, 2019 to 2020 and 2021 to 2022 collection years combined, for reception and for year 6.

School participation rates are shown as ranges:

• under 85%
• 85% to 90%
• 90% to 95%
• above 95%

The rates only included the years when measurements took place in the school during 2018 to 2019, 2019 to 2020 and 2021 to 2022.

Disclosure control applied to school and local authority-level data

School and local authority overweight and obesity prevalence is suppressed if the number of children in the category is 7 or less. The numerators and dominators used to calculate the prevalence and participation percentages have been rounded to the nearest 5. The prevalence and participation rates are calculated using these rounded values. This is in accordance with the NCMP disclosure control rules to ensure the data cannot be used to identify individual children.

Approach where schools have opened, closed or changed name during the previous 3 years

School data across the NCMP collection years has been combined using the Department for Education (DfE) unique reference number (URN) for each school. Where a URN has changed during this 3-year period (for example, when a school has changed to an academy), the DfE URN links table has been used to group data from the predecessor school with the new academy (downloaded from the Get Information about Schools website).

Comparison between school and England prevalence figures

The letters show a comparison of school overweight or obesity prevalence with the England prevalence value. These comparisons consider the 95% confidence intervals around the school and England prevalence figures where:

• the school prevalence is described as higher than the England average if prevalence of overweight and obesity in the school is higher than the England prevalence and the confidence intervals do not overlap
• the school prevalence is described as lower than the England average if prevalence of overweight and obesity in the school is lower than the England prevalence and the confidence intervals do not overlap
• the school prevalence is described as not statistically different to the England prevalence in all other cases where the confidence intervals around the school and England overweight and obesity prevalence overlap

Published NCMP analysis shows that prevalence of obesity is higher among boys than girls. As a result, schools that educate only boys, or have a higher proportion of boys than girls, are more likely to be flagged as having a higher prevalence, if compared with a comparator that includes both sexes. Therefore, a sex-standardised England comparator is used to make comparisons between school and England overweight and obesity prevalence. For example, in a school with 80% boys in reception, the reception overweight and obesity prevalence will be compared with an England value that weights the prevalence to 80% boys and 20% girls.

Contextualising the prevalence figures

To provide context for school prevalence data - particularly for schools with a prevalence of overweight or obesity that is lower than the England average - we have included the following text at the end of each letter:

In any population of children of all ages, it would be expected that 10% would be overweight and a further 5% living with obesity. However, current levels across England are far higher.

The overweight and obesity figures in this sentence have been taken from the UK90 growth reference for BMI that showed in the 1990 sample population that 10% of children were overweight and a further 5% were living with obesity.

Local authority and England data

Each letter includes data on the prevalence of overweight or obesity for the local authority of the school and England to help put the school data into context.

Data for City of London has been combined with Hackney and data for Isles of Scilly has been combined with Cornwall to ensure the data is non-disclosive.

The local authority and England prevalence figures are for 2018 to 2019, 2019 to 2020 and 2021 to 2022 collection years combined.

Recommended data quality checks for local authorities

It is strongly advised that local authorities perform quality checks on the individual letters before sending them to schools. Providing schools with accurate feedback letters helps to maintain confidence in the NCMP and continued engagement for future collection years.

The following information can be used to assist local authorities in quality checks:

1. Where schools have changed URN during the 2018 to 2019, 2019 to 2020 and 2021 to 2022 measurement years, it is possible that the local authority submitted data for both URNs and therefore more than one feedback letter will have been produced. Check that there is not more than one letter for these schools.
2. The local authority may have entered measurements erroneously where junior and infant schools are co-located. Specifically, reception records may have been submitted for a junior school or year 6 records may have been submitted for an infant school. Check that letters for infant and junior schools have the correct year groups presented.

If you have any queries about the production of data for the NCMP school feedback letters, contact ncmp@dhsc.gov.uk.