eprintid: 1553042 rev_number: 29 eprint_status: archive userid: 608 dir: disk0/01/55/30/42 datestamp: 2017-04-22 23:55:52 lastmod: 2021-12-02 23:19:37 status_changed: 2017-08-03 10:07:02 type: article metadata_visibility: show creators_name: Pennington, M creators_name: Gomes, M creators_name: Donaldson, C title: Handling Protest Responses in Contingent Valuation Surveys ispublished: pub divisions: UCL divisions: B02 divisions: D12 divisions: G21 keywords: EuroVaQ, Heckman selection, contingent valuation, missing data, multiple imputation note: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. 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. date: 2017-02-15 date_type: published official_url: http://doi.org/10.1177/0272989X17691771 oa_status: green full_text_type: other language: eng primo: open primo_central: open_green article_type_text: Journal Article verified: verified_manual elements_id: 1288747 doi: 10.1177/0272989X17691771 lyricists_name: Gomes, Manuel lyricists_id: MADEO09 actors_name: Gomes, Manuel actors_name: Stacey, Thomas actors_id: MADEO09 actors_id: TSSTA20 actors_role: owner actors_role: impersonator full_text_status: public publication: Medical Decision Making volume: 37 number: 6 pagerange: 623-634 event_location: United States issn: 1552-681X citation: Pennington, M; Gomes, M; Donaldson, C; (2017) Handling Protest Responses in Contingent Valuation Surveys. Medical Decision Making , 37 (6) pp. 623-634. 10.1177/0272989X17691771 <https://doi.org/10.1177/0272989X17691771>. Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/1553042/1/Gomes-M_handling%20protest%20responses_.pdf