Budget allocation is one of the most prominent matters of decision makers in health-care systems today. The allocation is a complex, multifaceted issue. One of the vital questions, related to the budget allocation, is how much health-care systems should spend on the improvement of health-related outcome in terms of one additional quality-adjusted life year (QALY). Common decision rules of economic evaluations indicate that an intervention is believed to be cost-effective if the incremental cost-effectiveness ratio (ICER) of cost-effectiveness analysis (CEA) falls below the cost-effectiveness threshold value. Generally, there are two main approaches to this value [1]. It can be seen as opportunity costs of new intervention in the health-care sector. If a commonly held view is taken, the threshold can be empirically assessed with preference elicitation methods, the most important of which is contingent valuation (CV).
CV is normally used to elicit monetary values of a non-market good or service [2] by requesting participants to state their willingness-to-pay (WTP) for obtaining a good, in this context, for QALY (always a small amount), which has been conducted in numerous studies [3–5]. Even though carefully considered CV research could yield helpful contributions to health-care decision-making, a set of questions requires further examination, regarding the most appropriate questionnaire format [6, 7]. Questionnaire format denotes the approach by which the respondent is required to provide their WTP, of which four classical techniques have been in use: open-ended (OE), closed-ended, payment card (PC) and bidding [8]. In contrast with environmental economics, where the closed-ended format has been largely utilized and was suggested as the ‘gold standard’ [9], the combination of the PC and the OE method has been used broadly in estimating WTP per QALY [3–5].
The PC technique was proposed by Mitchell [10] and first used in the general economics literature by Jones-Lee [11]. Respondents were given a specific range of monetary values and asked to select the maximum value they would be willing to pay for a particular benefit. On account of the good performance of imitating real life by letting respondents hesitate for their WTP, the PC has become a prevalent method of eliciting WTP in health economics.
The OE elicitation technique directly asks the respondent the maximum they would be willing to pay in a hypothetical scenario. Considering respondents tend to anchor on the proposed values when eliciting techniques imply value cues, the OE method can lead to a more precise and independent WTP value than other elicitation techniques, as it does not suggest an answer [12]. It was further verified that the OE format is an effective technique when the final decision depends on a quantile instead of the mean [13].
Given the popularity of the PC and the OE in health economics, more specifically, in estimating the monetary value of QALY, a plausible development is a direct comparison of these two formats. Although there is not any research comparing these two methods in estimating WTP/QALY, studies have examined the discrepancies of eliciting methods in other fields. A general finding is that for health-related goods, the OE format causes lower WTP values [14, 15]. However, for environmental goods [16] or an ambulance helicopter service [17], relatively equal values were reported.
The aim of this research is straightforward, taking focus on the comparison of the PC and the OE formats. First, we examined the difference of WTP/QALY estimates from these two methods. Furthermore, we investigated the theoretical validity of each method to determine which method elicits more valid monetary value of QALY.