Indications of Recruitment Challenges in Research with US Military Service Members: A ClinicalTrials.gov Review

Introduction: The success of military-relevant health research often depends on recruiting adequate numbers of U.S. military service members as research participants. Researchers have reported difficulties in recruiting service member research participants. Reviews of ClinicalTrials. gov, an online clinical trial registry of publicly and privately sponsored studies, have identified challenges in participant recruitment and barriers to study completion in various research populations. The purpose of this study was to identify indications of difficulty recruiting U.S. military service members as research participants based on data from study records in ClinicalTrials. gov. Materials and Methods: Records of studies starting between 2005 and 2014 were collected from ClinicalTrials. gov and updated through January 2016. Three hundred and two studies that included >= 25% U.S. military service member research participants were (1) compared to a comparison group of 302 studies, each with <5% service member participants and (2) compared by the proportion of service member participants within studies in the military group ("many" >= 25% but <100% service members and "all" 100% service members). Groups were evaluated and compared for recruitment status; reasons for study withdrawal, termination, or suspension; achievement of >= 85% of the anticipated enrollment; and differences in achieving recruitment goals according to study sponsor. Results: Twelve percent of studies in the military group had been withdrawn, terminated, or suspended; enrollment and funding problems were the most common reasons. The comparison group had 11% of studies withdrawn, terminated, or suspended; the most common reasons were enrollment problems and sponsor decision. All study groups had indications of difficulty adequately achieving participant enrollment goals. Among studies with known anticipated and actual enrollment, approximately half in both the military group (47.9%) and comparison group (50.3%) achieved >= 85% of the anticipated enrollment (p = 0.722). Half of studies with many service members and 44% of studies with all service members achieved >= 85% of the anticipated enrollment (p = 0.600). In comparing the many and all service member subgroups, significant differences were found in the median values for anticipated enrollment and actual enrollment, even when accounting for Bonferroni correction. Evaluations of mean values did not show a statistical difference between the military subgroups. There were no significant differences according to study sponsor (military, academic, Veterans Affairs, National Institutes of Health, nonprofit organization, or industry) for a study achieving or not achieving >= 85% of the anticipated enrollment. Conclusion: This review supports anecdotal reports of difficulty recruiting service members as research participants. However, the findings also indicate that in many regards, there is not much difference in the difficulties recruiting service members versus other research participants. Findings suggest that it is often difficult to recruit research participants regardless of the specific population or type of study sponsor, and that studies with either many or all service member participants have similar achievement of recruitment goals. Findings in this study may be useful for those who design research that includes service members or for those who are apprehensive about including service members in their research.