Online respondents less likely to understand the data linkage request, less likely to process the consent request thoroughly, and more likely to be concerned
about privacy and data security.

Using audio-recordings of the face-to-face interviews, we find that verbal behaviours of interviewers do not explain the mode effects: respondents only rarely ask questions or express concern, and interviewers only rarely offer additional information about the data linkage.

The devices respondents used to complete the web survey do not explain the mode effects either. Simplifying the consent request, by reducing the reading difficulty, increases understanding of the request, it does not increase consent in either mode.