The objective of this study was to determine the factors that cause divergences over time (differences) between stated willingness to pay (WTP) and actual WTP purchase behaviour;: and consider whether any divergence signifies the presence of bias in contingent valuation studies. Stated WTP for insecticide-treated bed-nets (ITNs) was elicited from a random sample of respondents using three question formats in Nigeria. The question formats were the bidding game (BG);: binary with follow-up (BWFU) and a novel structured haggling (SH) technique. The sales of the nets and a second survey were conducted 1 month after the first survey. In the second survey, factors that might explain the divergences were built into the questionnaire and these together with socio-economic variables were examined for causes of divergences in WTP. Data were analysed using non-parametric tests, testing of means and cross-tabulations.
Social Science and Medicine (2005) 60 (3) 525-536 [doi:10.1016/j.socscimed.2004.05.023]