MOSAiCH 2020: Mode of data collection The survey was conducted in a sequential mixed mode, where individuals were first asked to respond online. The option of responding on paper was then offered to include those who would not have access to the Internet or lack the necessary computer skills (push-to-web design). Sampling procedure and target population The nationally representative simple random sample for the survey comes from the sampling frame of the Federal Statistical Office (FSO) and is composed of individuals residing in Switzerland, living in a private household and aged 18 and over and speaking either German, French or Italian. Survey design and fieldwork The survey was fielded in two sequential parts. Only respondents having answered to part 1 were invited to part 2. The initial mode of contact was postal mail. Respondents were encouraged to provide a valid email address to facilitate contact for part 2. In both parts, the contact procedure comprised of a prenotification, invitation and three reminders. COVID19 survey wave 1 Mode and sample inclusion Most questions of wave 1 of the COVID-19 questionnaire were only included in the web version, as future waves would be conducted only on the web. Therefore, the first wave of the COVID-19 survey only includes respondents having participated to the MOSAiCH survey via web. Answers given on paper to some of the COVID-19 questions are included in the MOSAiCH 2020 data. Opt-out At the end of the web questionnaire, respondents were asked whether they would be willing to be recontacted for subsequent waves of the survey. Of the 2’093 respondents, 72.1% gave their consent. Weighting A simple weight was calculated to correct for non-response based on the information from the FSO sample. The variables used were age, gender, marital status, nationality, country of birth, urban/rural, NUTS 2 region and household size. Gross sample size MOSAiCH 2020: 10'152 Gross sample size COVID-19 w1: 3'290 respondents of MOSAiCH 2020 part 1 Valid interviews COVID-19 w1: 2093 in BETA version