WTP and WTA: do people think differently?

Contingent valuation (CV) studies in health care have used the willingness to pay (WTP) approach, to the virtual exclusion of willingness to accept (WTA). Outside the health care field, disparities between WTP and WTA values have been observed. Were such disparities to be demonstrated for health care technologies, the conventional assumption of a linear cost-effectiveness plane would be invalidated. This paper employs data derived from interviews with users of the UK's paediatric cochlear implantation (PCI) programme based in Nottingham (i) to assess the feasibility of estimating WTA for the potential discontinuation of an existing technology, and (ii) to investigate any WTA-WTP disparity which might be revealed. Only one-third of subjects providing WTP values were willing and able to offer a corresponding WTA value. Our qualitative data revealed that modes of response differed between the two valuation approaches. In particular, the presumption of fungibility of the health care intervention was a far more serious obstacle to completing the WTA task than it was for WTP. Among those prepared to offer values under both approaches, mean WTA was approximately four times mean WTP. Until more health studies are conducted, it remains unclear whether or not the findings are specific both to the intervention and to the elicitation format.