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The European Journal of Health Economics
Published in: The European Journal of Health Economics 6/2017

Open Access 01-07-2017 | Original Paper

The impact of the design of payment scales on the willingness to pay for health gains

Authors: Lotte Soeteman, Job van Exel, Ana Bobinac

Published in: The European Journal of Health Economics | Issue 6/2017

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Abstract

The questionnaire format applied in a CV study represents the way in which the WTP estimates are obtained. Payment scales are often used in CV studies as the questionnaire format of choice. The study summarized here analyzes the impact of the design of two payment scales (PS) on the monetary value of QALY gains. The scales differed in terms of their end-points, mid points, and coarseness. We judged the performance of the two PS against several indicators: the average WTP per QALY estimates, post-estimation uncertainty levels, the existence of mid-point concentration, and the dependency on end-points. Our results show that PS design influences respondents’ WTP values. The results also suggest that a more detailed scale with a more realistic range may help respondents to elicit values closer to their “true” WTP values, hence produce higher-quality outcomes. Further research and pretesting strategies are suggested to explore and minimize the effects of PS design on WTP estimates, which may ultimately increase the quality of WTP estimates.
Appendix
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Footnotes
1
Other studies have explored the effect of different types of scales (e.g., VAS scales, rating scales) on preferences and attitudes other than WTP, for example Lee et al. [38], Aguinis et al. [1], Hui and Triandis [33].
 
2
Here, the minimum and maximum values obtained using PS are primarily relevant as intervals surrounding OE values.
 
3
The 29 scenarios were obtained by combining 42 different EQ-5D states and four probability levels (i.e., 2, 4, 10, and 50 %), representing a fair spread of QALY gains across the utility plane. The scenarios were previously used in deriving the British [35] and Dutch [37] EQ-5D tariffs and used by Gyrd-Hansen [28] in her study of WTP per QALY in Denmark.
 
4
A visual aid using dots in explaining the concept of risk was demonstrated to increase the validity of WTP responses by Corso et al. [17]. Our design of this graphical explanation was similar to that used in the recent EuroVaQ project, see http://​research.​ncl.​ac.​uk/​eurovaq/​EuroVaQ_​Final_​Publishable_​Report_​and_​Appendices.​pdf.
 
5
The difference in OE-WTP values between PS-5 and PS-25 was approx. a factor three, but the difference in WTP per QALY values was approx. a factor 1.5. This was due to the “mean of ratios” method employed in the calculation (i.e., the mean of ratios calculated for each row of data), suggesting that respondents estimated OE-WTP values that are non-proportional to the size of the expected QALY gain. Employing the “ratio of means” method, on the contrary, would lead to a proportional difference (i.e., factor three), but would not account for the distribution of individual values.
 
6
With respect to the other variables presented in Table 3, the independent variable LN(health gain) is significant and positive, pointing to the theoretical validity of our findings, although non-proportional in relation, signaling scope insensitivity [8]. LN(income) was also significant: on average, in case a household income was 10 % higher, the respondents were willing to pay 6.9 % (i.e., 1.100.697) extra for the offered health gain.
 
7
For instance, if the “true” WTP value of a respondent is €50 for the offered health gain and the PS ranges from €0 to €500 with only 4 value points (e.g., 1, 100, 250, and 500) then the respondent needs to round her “true” value to the closest value point, either €1 or €100. Obviously, taking the either estimate as respondent’s WTP will lead to information loss and yield inaccurate WTP values (if inferred only from the PS, without OE-WTP).
 
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Metadata
Title
The impact of the design of payment scales on the willingness to pay for health gains
Authors
Lotte Soeteman
Job van Exel
Ana Bobinac
Publication date
01-07-2017
Publisher
Springer Berlin Heidelberg
Published in
The European Journal of Health Economics / Issue 6/2017
Print ISSN: 1618-7598
Electronic ISSN: 1618-7601
DOI
https://doi.org/10.1007/s10198-016-0825-y

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