Bias in cohort studies

Cohort studies allow an exploration of patient change over time. They can p rovide information on the incidence of disease, prognosis (including patien t satisfaction) and likely health-care resource use. Nonetheless, bias can be present in cohort studies in the way patients are selected and followed- up, the way measures are taken, or the way data are analysed. This short pa per explores ways in which such flaws can be uncovered in published studies , so that their findings can be interpreted appropriately.