Objectives: Examine the validity of using a self-completed Stated Preference Discrete Choice Modeling (SPDCM) questionnaire to measure parents' preferences for vaccinating their children against varicella.

Methods: A qualitative approach was used to assess the way parents understood the technical information in the questionnaire and the factors they considered to be important to the immunization decision. After completion of the SPDCM questionnaire, thirty-four participants completed a semistructured interview by telephone. Interview transcripts were analyzed by using content analysis. Comparisons were then made with the SPDCM questionnaire results.

Results: The technical information used to describe the program attributes appeared to be used appropriately by participants, although their explanations indicated that their understanding did not always come from the questionnaire information. Only one participant appeared to misunderstand the stated preference task, and a small number thought that the complexity and length should be reduced. The results of analysis of the questionnaire data were supported by the qualitative study, with the notable features of the model being reflected in the views commonly expressed about the immunization decision. Several additional factors were identified as important to the choice, including beliefs about vaccination generally and perceptions of the seriousness of varicella.

Conclusions: Although more research is required to investigate the validity of SPDCM for the measurement of preferences in health care, this study supports the validity of its use in childhood immunization where parents are familiar with the decision context.