• Sharea Ijaz, Jos H Verbeek, Christina Mischke, and Jani Ruotsalainen.
• Cochrane OSH Review Group, Finnish Institute of Occupational Health, PO Box 301, 70701 Kuopio, Finland.
• J Clin Epidemiol. 2014 Jun 1;67(6):645-53.

ObjectivesNonrandomized studies (NRSs) are considered to provide less reliable evidence for intervention effects. However, these are included in Cochrane reviews, despite discouragement. There has been no evaluation of when and how these designs are used. Therefore, we conducted an overview of current practice.Study Design And SettingWe included all Cochrane reviews that considered NRS, conducting inclusions and data extraction in duplicate.ResultsOf the included 202 reviews, 114 (56%) did not cite a reason for including NRS. The reasons were divided into two major categories: NRS were included because randomized controlled trials (RCTs) are wanted (N = 81, 92%) but not feasible, lacking, or insufficient alone or because RCTs are not needed (N = 7, 8%). A range of designs were included with controlled before-after studies as the most common. Most interventions were nonpharmaceutical and the settings nonmedical. For risk of bias assessment, Cochrane Effective Practice and Organisation of Care Group's checklists were used by most reviewers (38%), whereas others used a variety of checklists and self-constructed tools.ConclusionMost Cochrane reviews do not justify including NRS. When they do, most are not in line with Cochrane recommendations. Risk of bias assessment varies across reviews and needs improvement.Copyright © 2014 Elsevier Inc. All rights reserved.

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