Received wisdom in survey practice suggests that using web mode in the first wave of a panel study is not as effective as using interviewers. Based on data from a two-wave mode experiment for the Swiss Household Panel (SHP), this study examines how the use of online data collection in the first wave affects participation in the second wave, and if so, who is affected. The experiment compared the traditional SHP design of telephone interviewing to a mixed-mode design combining a household questionnaire by telephone with individual questionnaires by web and to a web-only design for the household and individual …