Out damn bot, out: Recruiting real people into substance use studies on the internet.

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.