RESUMO
A recent systematic review of the responsible gambling research suggests that there are no significant differences between gambling industry and non-industry funded research with regard to research design and outcomes. This study empirically synthesizes the outcomes of a larger sample of the scientific gambling literature to determine the generalizability of these original results. Our goal was to determine the extent to which funding sources might differentially influence characteristics of research design and outcomes. We conducted a comprehensive review of 18 research databases and examined studies published between January 2008 and August 2018. For four gambling-related journals, we reviewed all of the available studies. For 14 addiction-related journals, we examined only studies that examined gambling-related outcomes. To be included in this study, publications had to be quantitative and include a clear gambling-related hypothesis. After retrieving 1731 gambling studies, we applied the inclusion criteria and retained 720 studies for our final analytic sample. We used hypothesis confirmation and funding source information to determine the presence or absence of funding bias. Gambling industry funded studies were no more likely than studies not funded by the gambling industry to report either confirmed, partially confirmed, or rejected hypotheses. Nonetheless, studies funded by the gambling industry were more likely than other types of funding sources to include a conflict of interest statement. Studies with disclosed funding sources were more likely than those with undisclosed funding sources to include a conflict of interest statement. These findings highlight the importance of transparency and disclosure during research dissemination.