Objective To investigate the impact of patient and public involvement (PPI) on rates of enrollment and retention in clinical trials and explore how this varies with the context and nature of PPI.
Design Systematic review and meta-analysis.
Data sources Ten electronic databases, including Medline, INVOLVE Evidence Library, and clinical trial registries.
Eligibility criteria Experimental and observational studies quantitatively evaluating the impact of a PPI intervention, compared with no intervention or non-PPI intervention(s), on participant enrollment and/or retention rates in a clinical trial or trials. PPI interventions could include additional non-PPI components inseparable from the PPI (for example, other stakeholder involvement).
Data extraction and analysis Two independent reviewers extracted data on enrollment and retention rates, as well as on the context and characteristics of PPI intervention, and assessed risk of bias. Random effects meta-analyses were used to determine the average effect of PPI interventions on enrollment and retention in clinical trials: main analysis including randomized studies only, secondary analysis adding non-randomized studies, and several exploratory subgroup and sensitivity analyses.
Results 26 studies were included in the review; 19 were eligible for enrollment meta-analysis and five for retention meta-analysis. Various PPI interventions were identified with different degrees of involvement, different numbers and types of people involved, and input at different stages of the trial process. On average, PPI interventions modestly but significantly increased the odds of participant enrollment in the main analysis (odds ratio 1.16, 95% confidence interval and prediction interval 1.01 to 1.34). Non-PPI components of interventions may have contributed to this effect. In exploratory subgroup analyses, the involvement of people with lived experience of the condition under study was significantly associated with improved enrollment (odds ratio 3.14 v 1.07; P=0.02). The findings for retention were inconclusive owing to the paucity of eligible studies (odds ratio 1.16, 95% confidence interval 0.33 to 4.14), for main analysis).
Conclusions These findings add weight to the case for PPI in clinical trials by indicating that it is likely to improve enrollment of participants, especially if it includes people with lived experience of the health condition under study. Further research is needed to assess which types of PPI work best in particular contexts, the cost effectiveness of PPI, the impact of PPI at earlier stages of trial design, and the impact of PPI interventions specifically targeting retention.