Fig. 1

Flow chart of study procedures. Superscript digit 1 indicates the following: if patients did not want to participate in the study, they had to actively sign out. Otherwise, they would receive an invitation (and later reminders) for the first questionnaire. Superscript digit 2 indicates the following: it was explained that filling in the questionnaire meant giving permission to use the data for the study. Patients could also sign-up their own control subject in the first questionnaire