*2.2. Study Design and Data Collection*

The cross-sectional study was conducted between 1 March and 10 May 2021. The invitations were sent to official e-mail addresses published on the websites of all University of the Third Age chapters in Poland. In this study, the snowball sampling method was employed; it is a non-random sample selection method consisting in recruiting participants by other participants (in our study by the Presidents of Universities of the Third Age or substantive coordinators the Universities that offer such forms of education for the older adults). We used this method in our study as we did not have a contact database for direct students of Universities of the Third Age.

The study involved an online survey created using dedicated software (Webankieta) (Get Feedback, Warsaw, Poland). A link to the survey was included in the invitation e-mails sent to the addresses available on the official University websites. The responses were recorded on the platform, and then downloaded as raw data prepared for a statistical analysis. The mean time to complete the survey was 29 min.

Apart from age and enrolment in the University of the Third Age programme, an additional inclusion criterion was written informed consent to participate in the study. The exclusion criteria were: (1) age ≤ 60 years; (2) illiteracy (a respondent who had completed at least primary school could participate in the study); and (3) lack of written consent to participate in the study. Each participant could withdraw from the study at any time.

The respondents were chosen by nonprobability sampling. Taking into account the total number of returned questionnaires, the rate of complete filling was 52.7%. The remaining questionnaires were incomplete (47.3%).
