Introducing a web option in interviewer-administered surveys could increase response rates and reduce costs. However, this requires careful assessment of the effects of mixed-mode designs on data quality and key measures, especially across important sociodemographic subgroups. In 2018 and 2020, the Health and Retirement Study (HRS) experimentally introduced web in a sequential mixed-mode design for panelists assigned to the telephone mode. Initial analyses found a limited number of mode effects on key outcome distributions and data quality measures. This paper extends this initial analysis by assessing possible heterogeneity in these effects among sociodemographic subgroups defined by race/ethnicity, sex, and others. We interact mode with each sociodemographic indicator in statistical models for each outcome. Overall, we found limited evidence of heterogeneity in the mode effects, with 3% of the 204 interaction terms we tested emerging as significant. For example, previous work showed that more household roster changes are reported in the web-first group, and we found that this was more pronounced for females and those with some college education. Although some heterogeneity in mode effects was observed across subgroups, the effects were generally too small to cause data quality concerns. We conclude with a discussion of broader considerations for survey researchers.
Schroeder et al. (2026) studied this question.