Accessing hidden populations: Advertisements on social networking websites for cost-effective participant recruitment

Background: The ability of researchers to carry out investigations can be limited by their ability to access populations of interest. Innovations in participant recruitment are needed to enable researchers to carry out studies in timesaving and cost-effective ways. Methods: An advertising campaign was displayed on a popular social networking website to recruit pregnant women for an online survey. Ads were targeted such that they were shown only to individuals who met some of the inclusion criteria (i.e., female, aged 18-44, living in the United States). The self-service application provided by the social networking website allowed the investigator to create the ads, manage expenditures, and track usage metrics on an as-needed basis. Results: Over the course of 18 weeks the ads were shown 10,577,381 times to 7,248,985 unique users of the social networking site. The ads received 6,094 clicks by 5,963 unique users for a unique click-through rate of 0.08% at a mean cost of $0.63 per click. Eighteen percent (18%, n = 1,075) of those who clicked on a recruitment ad consented to participate. Strict additional eligibility criteria reduced the respondent pool to a final count of 344 women. The total cost of the campaign was $3,821.81 or $11.11 per participant. Conclusions: A national sample of nulliparous women in the first 20 weeks of pregnancy was obtained successfully at a reasonable cost and with only modest technological expertise. Highly targeted online ads are a cost-effective method for reaching hidden or otherwise difficult-to-access populations for public health nursing research.