2.1. Procedure

The current study was approved by the Regional Ethical Committee in Stockholm, Sweden (2017-1926-32). The survey was conducted as part of a collaboration between Stockholm University and Ålands Penningautomatförening (Paf), a publicly governed gambling operator in the Åland Islands (Finland), which runs the online gambling platform paf.com providing slot-games, poker, betting, casino games, and bingo. After development and pilot-testing of the survey (see Section 2.3), data collection began on 20 February 2018 and closed on March 1st 2018, with one reminder sent out on 26 February 2018 to 8826 customers. The questionnaire was distributed by email from paf.com to the email address connected to the customer's user account. In the email, customers were informed of the purpose of the survey, the collaboration between Paf and Stockholm University, the option of ceasing their participation at any time, and the possibility of winning a gift card from verkkokauppa.com (see Appendix A). The gift card could not be exchanged for money and could not be used to buy gambling services. One 50-euro gift card was raffled for every group of 100 respondents. The customers were also provided contact information to Paf's customer support. The pilot and the finalized questionnaire included detailed information about the project, the handling of personal data, the ethical approval, the right to stop participating, and contact information to the project team at Stockholm University and Paf's customer support (see Appendix B). The content of the reminder was identical to the initial mailing. Prior to completing the questionnaire, customers could agree to participate (whereupon they were enrolled in the study) or not (their answers were deleted). The winners of gift cards were chosen randomly and contacted by email.