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Table 6 Checklist to determine the potential risk of bias in observational studies

From: Risk of bias in observational studies using routinely collected data of comparative effectiveness research: a meta-research study

Guiding question Explanation
1. When does the follow-up start? - Check if the authors report the start of follow-up. It might be called the baseline, index date, and time zero.
2. When do individuals complete eligibility? - Check if authors report when individuals should complete eligibility.
 2.a. Can individuals be eligible at multiple times? - Check if individuals could be eligible at multiple times and whether authors used a strategy to overcome this: (1) choose a single eligible time and (2) choose all eligible times and conduct a sequence of trials at each eligible time.
 2.b. Is there any post-baseline event (i.e., an event after the follow-up starts) in the eligibility criteria? - Check if any events after the start of follow-up are listed in the eligibility criteria, e.g., complete 2 consecutive prescriptions or no outcome for the first 2 months after the start of follow-up.
3. When are individuals assigned to an exposed or non-exposed group? - Check if the authors report clearly when individuals are classified as exposed or non-exposed group.
 3a. Do individuals have to use treatment for a given period to be classified as an exposed group? - Check if individuals have to use treatment for a given period, e.g., complete 2 consecutive prescriptions to be classified as exposed and non-exposed, if not, start the treatment or complete only 1 prescription.
 3.b. Is there a grace period? - Check if individuals can start the treatment sometime after the start of follow-up and eligibility.