Principal Findings
RECRUITMENT
We reached over 30,000 Facebook users, and close to 10,000 adults clicked on our Facebook advertisement. From these clicks, we enrolled 32% (32/100) of our required study sample in only 5 months, and spent US $51.94 per participant who ultimately signed the ICF. This sample came from 17 different states, with ages ranging from 46 to 77 years (mean 59.8 years), with more women (n=24, 75%) than men (n=8, 25%), and more White (n=28, 88%) than Black or African Americans (n=3, 9%) and Asians (n=1, 3%). These findings point to social media being a useful and efficient avenue to recruit and enroll participants with knee OA within the United States into a telehealth physical therapy study.We observed a steep drop-off from clicks to actual enrollment. In other words, a large portion of participants did not fill out the screening form after being redirected to the survey link as we had 9879 clicks, but only 423 (4.3%) filled out the screening form. Although speculative, these participants may have clicked on the link without carefully reading the advertisements, or they may have lost interest after reading the full study description. Developing credibility and trust with an investigative team is an important element for clinical trials, and the absence of additional channels (eg, email and phone number) to contact the research team may have eroded the participant’s confidence and trust with the integrity of the study [Similar drop-off was reported by Reagan et al [Our recruitment costs were far less than traditional methods. Our average recruitment cost of US $51.94 per participant is well below figures presented by Tate et al [A notable aspect of our sample was that it represented 17 different states within the United States, with approximately one-third coming from predominantly rural-area states. Correspondingly, a recent US-based study that included remotely delivered interventions found that virtually recruited strategies yielded a larger number of states (average of 24.4 states) compared to traditionally recruited strategies (average of 1.1 states) [We find it notable that our average age was 59.8 years, with most participants (41%, n=13) falling into the 55-64 years age category. Moreover, we recruited more women than men, and the average age of our sample was 59.8 (SD 8.4) years. These findings are consistent with a previous unpublished study, which successfully recruited adults older than 40 years with OA from Facebook for a clinical trial [