Criterion and content validity of a novel structured haggling contingent valuation question format versus the bidding game and binary with follow-up format.

Contingent valuation question formats that will be used to elicit willingness to pay for goods and services need to be relevant to the area they will be used in order for responses to be valid. A novel contingent valuation question format called the "structured haggling technique" (SH) that resembles the bargaining system in Nigerian markets was designed and its criterion and content validity compared with those of the bidding game (BG) and binary-with-follow-up (BWFU) technique. This was achieved by determining the willingness to pay (WTP) for insecticide-treated nets (ITNs) in Southeast Nigeria. Content validity was determined through observation of actual trading of untreated nets together with interviews with sellers and consumers. Criterion validity was determined by comparing stated and actual WTP. Stated WTP was determined using a questionnaire administered to 810 household heads and actual WTP was determined by offering the nets for sale to all respondents one month later. The phi (correlation) coefficient was used to compare criterion validity across question formats. The phi coefficients were SH (0.60: 95% C.I. 0.50-0.71), BG (0.42: 95% C.I. 0.29-0.54) and the BWFU (0.32: 95% C.I. 0.20-0.44), implying that the BG and SH had similar levels of criterion-validity while the BWFU was the least criterion-valid. However, the SH was the most content-valid. It is necessary to validate the findings in other areas where haggling is common. Future studies should establish the content validity of question formats in the contexts in which they will be used before administering questionnaires.