Hypothesis 1: Problem gamblers who receive the personalized feedback intervention will reduce their gambling more than problem gamblers who do not receive any intervention (waiting list control condition) by a six-month follow-up.Hypothesis 2: The effect of the intervention will be sustained through the 12-month follow-up.Hypothesis 3 (mediator hypothesis): Respondents in the intervention condition who report greater reductions in their estimates about how much others gamble between baseline and three-month follow-up will demonstrate more improvement in gambling outcomes at six-month follow-up, compared to respondents in the intervention condition who report smaller reductions in their perceived gambling norms.