Series: Pragmatic trials and real world evidence : Paper 3. Patient selection challenges and consequences

This paper addresses challenges of identifying, enrolling and retaining participants in a in a trial conducted within a routine care setting. All patients that are potential candidates for the treatments in routine clinical practice should be considered eligible for a pragmatic trial. To ensure generalizability, the recruited sample should have a similar distribution of the treatment effect modifiers as the target population. In practice this can be best achieved by including - within the selected sites - all patients without further selection. If relevant heterogeneity between subgroups is expected, increasing the relative proportion of the subgroup of patients in the heterogeneous trial could be considered (oversampling), or a separate trial in this subgroup can be planned. Selection will nevertheless occur. Low enrolment and loss to follow-up can introduce selection and can jeopardize validity as well as generalizability. Pragmatic trials are conducted in clinical practice rather than in a dedicated research setting, which could reduce recruitment rates. However, if a trial poses a minimal burden to the physician and the patient, and routine clinical practice is maximally adhered to, the participation rate may be high and loss to follow-up will not be a specific problem for pragmatic trials