Strenghts and limitations
Our study has a number of strengths. First, we investigated recruitment failure in 83 RCTs embedded within the Dutch Consortium for Women’s Health Research – and thus within one discipline - with support and monitoring by the clinical trial centre. This allowed us to standardize several important aspects, like trial management and logistics, data collection and data monitoring. Second, we were able to assess all indicators with a potential association with poor recruitment as described in literature; type of investigation, placebo-controlled study, treatment versus no treatment, whether the intervention was new or only available in the trial, whether the study was blinded or if there were any competing RCTs, number of study arms, number of inclusion and exclusion criteria, whether a pilot study was performed, number of participating centres and funding and compensation per included patient.
The main limitation of our study is the number of trials. Obviously, if we could have accessed an even larger cohort of trials, we might have been able to identify more potential indicators for recruitment failure. A further limitation may be that within our study we focussed on objective indicators, such as trial logistics and design issues. Other aspects, like patients’ or practitioners’ perspectives, which may affect recruitment as well were beyond the scope of our study.