Invited commentary: recruiting for epidemiologic studies using social media.

Social media-based recruitment for epidemiologic studies has the potential to expand the demographic and geographic reach of investigators and identify potential participants more cost-effectively than traditional approaches. In fact, social media are particularly appealing for their ability to engage traditionally "hard-to-reach" populations, including young adults and low-income populations. Despite their great promise as a tool for epidemiologists, social media-based recruitment approaches do not currently compare favorably with gold-standard probability-based sampling approaches. Sparse data on the demographic characteristics of social media users, patterns of social media use, and appropriate sampling frames limit our ability to implement probability-based sampling strategies. In a well-conducted study, Harris et al. (Am J Epidemiol. 2015;181(10):737-746) examined the cost-effectiveness of social media-based recruitment (advertisements and promotion) in the Contraceptive Use, Pregnancy Intention, and Decisions (CUPID) Study, a cohort study of 3,799 young adult Australian women, and the approximate representativeness of the CUPID cohort. Implications for social media-based recruitment strategies for cohort assembly, data accuracy, implementation, and human subjects concerns are discussed.