Rationale & objectives: Different question formats elicit different willingness-to-pay (WTP) results, but there is no consensus on which method elicits the most valid WTP. In spite of the methodological controversies, WTP is a potentially valuable tool in health economics to value health services. Our general objective was to provide additional evidence on the validity of two WTP elicitation formats: the open-ended question and the payment scale.
Methods: We elicited WTP for a hearing aid among hearing aid users (n = 108), using both a payment scale and an open-ended question. We compared the results from both formats. We tested criterion validity by comparing both formats with the actual out-of-pocket payment. Construct validity was tested by examining whether WTP was consistent with positive income elasticity.
Results: The WTP results elicited with the payment scale and open-ended question were not statistically significantly different. Both formats showed good criterion validity, although the open-ended question showed a stronger association with the actual out-of-pocket payment. The open-ended format showed better construct validity, as it was influenced by family income.
Conclusion: The results of the present study showed that the open-ended question was more valid than the payment scale question. We, therefore, recommend that in future WTP studies on hearing aids the open-ended question is used to directly elicit WTP values. The same recommendation may apply to other studies where respondents are familiar with costs or payments for the intervention under evaluation.