Cost attribute in health care DCEs: Just adding another attribute or a trigger of change in the stated preferences?

This paper investigated the effects of including an opt-out option and the cost attribute on the elicited preference structure and response error variance in a discrete choice experiment (DCE) valuing the preferences for the delivery of dental care. The mixed logit framework was used for testing the effects of survey design features on respondents' preferences and scale. The standard practice of testing these effects was further expanded by using the structural choice modelling (SCM) framework. Recent studies have suggested that not offering respondents an opt-out option may distort the utility estimates. However, the influence of the opt-out option, framed as a ‘substitute care provider’ alternative, on the preferences for dental care and response error variance was not significant. When the cost attribute was added to the choice sets, the rank order of the attributes remained the same, and overall preferences did not differ significantly. This indicates that respondents did not change their decision rule. However, they were not very consistent in their preferences for all attributes. Including an extra cost attribute significantly increased the response error variance. The findings indicate that the cost attribute could be safely used, at least in similar contexts, without concerns for disturbing the preferences for other attributes. We did not find strong evidence that the effect of including an extra cost attribute is any different from the expected effect of including any other choice attribute; therefore, its influence may not be as relevant as some of the previous studies may have suggested.