Impact of study design on recruitment of patients to a primary care trial: an observational time series analysis of the Birmingham Atrial Fibrillation Treatment of the Aged (BAFTA) study.

BACKGROUND: recruitment targets to randomized controlled trials (RCTs) are often not met. Many interventions are used to improve recruitment but there is little empirical evidence on whether these approaches work. OBJECTIVE: to examine whether changes to the design and conduct of a primary care-based RCT were associated with changes in patient recruitment. METHODS: an observational time series analysis of recruitment to a primary care-based multi-centre RCT of aspirin versus warfarin for stroke prevention, which involved 330 practices. Several changes to the trial protocol and procedures were made over the 4 years of patient recruitment. For each quarter throughout the recruitment period, the recruitment rate per 1000 total population in active practices was calculated. RESULTS: the recruitment target of 930 patients was exceeded. Fluctuations in recruitment rate occurred during the recruitment period. Following protocol changes aimed to reduce clinical workload, there was a significant increase in recruitment during the final 6 months of the study, during a period when there was not a similarly large increase in the total population available. CONCLUSIONS: these findings suggest that the conduct of a trial is an important consideration if studies are to recruit successfully. Expanding the number of centres may not be the most effective way to improve recruitment.