Recruitment and adherence of randomized controlled trials for mild cognitive impairment: A systematic review and meta-analysis

Objectives The recruitment and adherence status of randomized controlled trials (RCTs) for population with mild cognitive impairment (MCI) are little known. We aimed to explore the RCT recruitment and adherence status and factors associated with these among MCI patients. Methods We searched MEDLINE, EMBASE, Cochrane Library, CINAHL, PsycINFO, and PsycARTICLES from inception to 8th July 2019. Included studies were RCTs conducted among MCI patients with available data of invitation rate, eligibility rate, randomization rate, recruitment rate, adherence rate, satisfaction rate, or potential barrier for recruitment and compliance. Two authors screened the studies and extracted the data independently. We calculated pooled proportions of each rate and their 95% confidence intervals (CIs) using random-effects meta-analysis. Meta-regression and subgroup analysis was conducted. Results Hundred and ten articles were judged to meet the study inclusion criteria from 10 387 articles. The invitation rates ranged from 9% to96% but were not pooled together due to high heterogeneity. The pooled overall eligibility, randomization, recruitment, intervention adherence, and follow-up adherence rates were 55% (95% CI: 48%-62%), 86% (95% CI: 81%-91%), 44% (95% CI: 37%-50%), 88% (95% CI: 86%-90%), and 85% (95% CI: 83%-87%), respectively. Non-MCI (47.5%), disease or medical problems (13.8%), and loss of interest (8.5%) were the most frequent reasons for screen failure. Refusal without reason (36.6%), adverse events (30.9%), and health issues (7.7%) were the most frequent reasons for drop-out. Conclusions This study provided important information for future RCTs targeting at MCI patients. Strategies designed to improve participant recruitment and RCT adherence should be developed among this population.