Rationale and protocol for a prospective clinical trial enrollment improvement hybrid study within a trial.

Introduction: Enrollment to clinical trials is challenging, and few evidence-based interventions to improve enrollment exist. Provider-facing advertising campaigns could help increase enrollment, but this type of intervention has not been prospectively evaluated in a clinical trial. Methods: We designed a randomized clinical trial to evaluate the effect of a month-long email advertising campaign on enrollment to a clinical trial. This hybrid implementation-effectiveness Study Within a Trial tested the effect of precision audit and feedback techniques enrollment effectiveness outcomes (enrollment) and measured implementation outcomes (email opens, link clicks). This design is an application of a Study Within a Trial (SWAT) to evaluate an intervention intended to improve enrollment. The goal of this study was to inform both this advertising campaign and refine SWAT methods for evaluating future trial improvement interventions. Discussion: This Study Within a Trial provides preliminary data on the effectiveness of email advertising campaigns for improving clinical trial enrollment. Additionally, the infrastructure built through this SWAT will inform future studies of clinical trial enrollment improvement. This protocol can serve as a template for other investigators seeking to evaluate enrollment improvement interventions.