What are the risks of bias associated with indirectness in research studies?
The risks of bias associated with indirectness in research studies include selective outcome reporting, recruitment bias in cluster-randomised trials, lack of washout periods to avoid carry-over effects in crossover trials, and use of unvalidated patient-reported outcome measures. Indirectness can also lead to systematic attrition bias if the missing data are likely to be different from the data of those remaining in the groups, and there is a differential rate of such missing data from groups. Additionally, indirectness can contribute to a difference in effect size, or may affect the balance of harms and benefits considered for an intervention.