From: Enrollment, retention, and strategies for including disadvantaged populations in randomized controlled trials: a systematic review protocol
Are the characteristics of the patients included in the study clearly described?
Have the characteristics of patients lost to follow-up been described?
Were those subjects who were prepared to participate representative of the entire population from which they were recruited?
Were the patients in different intervention groups (trials and cohort studies) or were the cases and controls (case-control studies) recruited from the same population?