Self-rated health assessed by web versus mail modes in a mixed mode survey: the digital divide effect and the genuine survey mode effect.

OBJECTIVE: To investigate differences in self-rated health (SRH) between web and mail questionnaires in a mixed mode survey and to provide a model that explains those differences.
SUBJECTS: A total of 15,200 mail respondents and 17,829 web respondents from the 2008 US National Health Survey conducted by the Gallup Panel. RESEARCH
DESIGN: Respondents were recruited using random digit dialing and assigned to one of the two survey modes (web or mail). Respondents with household Internet connection and frequent Internet usage were invited to complete the survey through the web mode. Respondents who had no Internet connection or who used the Internet infrequently were invited to the mail mode. Thus, respondents with better Internet access used the web mode. MEASURES: Respondents completed a questionnaire that asked about SRH status, objective health conditions, health behaviors, and other socioeconomic variables. Statistical associations were analyzed with ordered Logit and negative binomial models.
RESULTS: Web respondents reported better SRH than mail respondents. This difference is in part reflective of variability in objective health status between these two groups, and in part attributable to the effects of survey mode. These results maintained with age controlled.
CONCLUSIONS: The alignment between survey mode selection, Internet access, and health disparities, as well as genuine survey mode characteristics, leads to web-mail differences in SRH. Unless the digital divide and its influences on survey mode selection are resolved and differential genuine mode effects are fully comprehended, we recommend that both modes be simultaneously used on a complementary basis.