While the Internet has become a popular and effective strategy for recruiting substance users into research, there is a large risk of recruiting duplicate individuals and Internet bots that pose as humans. Strategies to mitigate these issues are outlined and categorized into two groups: (1) automatic techniques which are often embedded into surveys and (2) ongoing manual techniques implemented during recruitment. Potential limitations of these strategies are discussed, and an example of the prevalence of duplicate data within a substance using sample is provided. Overall, it is recommended that researchers consider the use of routine strategies to mitigate the risks associated with recruiting online samples such as: verifying participant contact information, IP address checks, and ongoing cross-checking of participant information for duplicates, similarities and inconsistencies.

Background and aimsThe current randomized controlled trial tested whether there was benefit to providing an online gambling intervention and a separate self-help mental health intervention for anxiety and depression (i.e. MoodGYM) (G + MH), compared to only a gambling intervention (G only) among people with co-occurring gambling problems and mental health distress. The primary outcome of interest was improvement in gambling outcomes. Secondary analyses also tested for the impact of the combined intervention on depression and anxiety outcomes.MethodsParticipants who were concerned about their gambling were recruited to help evaluate an online intervention for gamblers. Those who met criteria for problem gambling were randomized to receive either the G only or the G + MH intervention. Participants were also assessed for current mental health distress at baseline, with three quarters (n = 214) reporting significant current distress and form the sample for this study. Participants were followed-up at 3- and 6-months to assess changes in gambling status, and improvements in depression and anxiety.ResultsFollow-up rates were poor (47% completed at least one follow-up). While there were significant reductions in gambling outcomes, as well as on measures of current depression and anxiety, there was no significant difference in outcomes between participants receiving the G only versus the G + MH intervention.Discussion and conclusionThere does not appear to be a benefit to providing access to an additional online mental health intervention to our online gambling intervention, at least among participants who are concerned about their gambling.Trial registration: ClinicalTrials.govNCT02800096; Registration date: June 14, 2016.

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