OBJECTIVES : The lack of evidence about the external validity of discrete choice experiments (DCEs) is one of the barriers that inhibits greater use of DCEs in healthcare decision-making. This study examines external validity of DCE-derived preferences, unravel its determinants, and provide evidence whether healthcare choice is predictable.

METHODS : A six-step approach in the area of influenza vaccination was used: i) a literature study, ii) expert interviews, iii) focus groups, iv) a DCE, v) field data, and vi) in-depth interviews with respondents who showed discordance between stated preferences and actual healthcare utilization. Respondents without missing values in the DCE and the field data (377/499=76%) were included in the analyses. Random-utility-maximization and random-regret-minimization choice processes were used to analyze the DCE data, whereas the interviews combined five scientific theories to explain discordance.

RESULTS : When models took into account scale and preference heterogeneity, real-world choices to opt for influenza vaccination were correctly predicted by DCE at an aggregate level, and almost 90% of choices were correctly predicted at an individual level. There was 13% (49/377) discordance between stated preferences and actual healthcare utilization. In-depth interviews showed that several dimensions played a role in clarifying this discordance: attitude, social support, action of planning, barriers, and intention.

CONCLUSIONS : Evidence was found that DCE can yield accurate predictions of real-world behavior if at least scale and preference heterogeneity are taken into account. Analysis of discordant subjects showed that we can even do better. DCE measures an important part of preferences by focusing on attribute tradeoffs that people make in their decision to participate in a healthcare intervention. Inhibitors may be among these attributes, but it is more likely that inhibitors have to do with exogenous factors like goals, phobias, and social norms. Conducting upfront work on constraints/inhibitors of the focal behavior might further improve predictive ability.