BMJ  2005;330:895-897 (16 April), doi:10.1136/bmj.330.7496.895

Education and debate

Reader's guide to critical appraisal of cohort studies: 1. Role and design

¹ Kunin-Lunenfeld Applied Research Unit, Baycrest Centre for Geriatric Care, Toronto, ON, Canada, ² Meyers Primary Care Institute, Worcester, MA 01605, USA, ³ Institute for Clinical Evaluative Sciences, Toronto, ON, Canada, ⁴ Department of Psychiatry, University of Toronto, Toronto, ON, Canada, ⁵ Department of Health Care Policy, Harvard Medical School, Boston, USA, ⁶ Department of Health Policy, Management, and Evaluation, Faculty of Medicine, University of Toronto, Toronto, ON, Canada

Cohort studies can provide valuable information unavailable from randomised trials, but readers need to be alert to possible flaws

The first 150 words of the full text of this article appear below.

Introduction

Valid evidence on the benefits and risks of healthcare interventions is essential to rational decision making. Randomised controlled trials are considered the best method for providing evidence on efficacy. However, they face important ethical and logistical constraints and have been criticised for focusing on highly selected populations and outcomes.^{1 2} Some of these problems can be overcome by cohort studies. Cohort studies can be thought of as natural experiments in which outcomes are measured in real world rather than experimental settings. They can evaluate large groups of diverse individuals, follow them for long periods, and provide information on a range of outcomes, including rare adverse events. However, the promise of cohort studies as a useful source of evidence needs to be balanced against concerns about the validity of that evidence.^{3 4}

In this three paper series we will provide an approach to the critical appraisal of cohort studies. This article describes the . . . [Full text of this article]

Randomised trial or cohort study?

Selection bias as a threat to validity

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Comparison groups in cohort studies

Questions to ask when assessing a cohort study design

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