Handling protest responses in contingent valuation surveys

Mark Pennington, Manuel Gomes, Cam Donaldson

Research output: Contribution to journalArticle

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Abstract

Objectives
Protest responses, whereby respondents refuse to state the value they place on the health gain, are commonly encountered in contingent valuation (CV) studies, and they tend to be excluded from analyses. Such an approach will be biased if protesters differ from non-protesters on characteristics that predict their responses. The Heckman selection model has been commonly used to adjust for protesters, but its underlying assumptions may be implausible in this context. We present a multiple imputation (MI) approach to appropriately address protest responses in CV studies, and compare it with the Heckman selection model.

Methods
This study exploits data from the multinational EuroVaQ study, which surveyed respondents’ willingness-to-pay (WTP) for a Quality Adjusted Life Year (QALY). Here, our simulation study assesses the relative performance of MI and Heckman selection models across different realistic settings grounded in the EuroVaQ study, including scenarios with different proportions of missing data and non-response mechanisms. We then illustrate the methods in the EuroVaQ study for estimating mean WTP for a QALY gain.

Results
We find that MI provides lower bias and mean squared error compared with the Heckman approach across all considered scenarios. The simulations suggest that the Heckman approach can lead to considerable underestimation or overestimation of mean WTP due to violations in the normality assumption, even after log-transforming the WTP responses. The case study illustrates that protesters are associated with a lower mean WTP for a QALY gain compared with non-protesters, but that the results differ according to method for handling protesters.

Conclusions
MI is an appropriate method for addressing protest responses in CV studies.
Original languageEnglish
Pages (from-to)626-634
Number of pages9
JournalMedical Decision Making
Volume37
Issue number6
Early online date15 Feb 2017
DOIs
Publication statusPublished - Aug 2017

Fingerprint

Quality-Adjusted Life Years
willingness to pay
protest
scenario
simulation
response behavior
normality
Health
Surveys and Questionnaires
Willingness-to-pay
Heckman
Protest responses
Contingent valuation
trend
health
performance
Multiple imputation
Selection model
Quality-adjusted life years
Values

Keywords

  • contingent valuation
  • economics
  • EuroVaQ
  • Heckman selection
  • multiple imputation
  • missing data

Cite this

Pennington, Mark ; Gomes, Manuel ; Donaldson, Cam. / Handling protest responses in contingent valuation surveys. In: Medical Decision Making. 2017 ; Vol. 37, No. 6. pp. 626-634.
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Handling protest responses in contingent valuation surveys. / Pennington, Mark; Gomes, Manuel; Donaldson, Cam.

In: Medical Decision Making, Vol. 37, No. 6, 08.2017, p. 626-634.

Research output: Contribution to journalArticle

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N2 - ObjectivesProtest responses, whereby respondents refuse to state the value they place on the health gain, are commonly encountered in contingent valuation (CV) studies, and they tend to be excluded from analyses. Such an approach will be biased if protesters differ from non-protesters on characteristics that predict their responses. The Heckman selection model has been commonly used to adjust for protesters, but its underlying assumptions may be implausible in this context. We present a multiple imputation (MI) approach to appropriately address protest responses in CV studies, and compare it with the Heckman selection model.MethodsThis study exploits data from the multinational EuroVaQ study, which surveyed respondents’ willingness-to-pay (WTP) for a Quality Adjusted Life Year (QALY). Here, our simulation study assesses the relative performance of MI and Heckman selection models across different realistic settings grounded in the EuroVaQ study, including scenarios with different proportions of missing data and non-response mechanisms. We then illustrate the methods in the EuroVaQ study for estimating mean WTP for a QALY gain.ResultsWe find that MI provides lower bias and mean squared error compared with the Heckman approach across all considered scenarios. The simulations suggest that the Heckman approach can lead to considerable underestimation or overestimation of mean WTP due to violations in the normality assumption, even after log-transforming the WTP responses. The case study illustrates that protesters are associated with a lower mean WTP for a QALY gain compared with non-protesters, but that the results differ according to method for handling protesters.ConclusionsMI is an appropriate method for addressing protest responses in CV studies.

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