Figure 1. Comparison of the results of 8000 randomized, controlled trials (RCTs) and 8000 historical controlled studies (HCTs) obtained from resampling within the European Carotid Surgery Trial. The distribution of results indicates systematic bias (average odds ratios in the randomized, controlled trials and historical controlled studies were 1.23 and 1.06, respectively). Adapted with permission from reference 27: Deeks JJ, Dinnes J, D'Amico R, Sowden AJ, Sakarovitch C, Song F, et al. Evaluating non-randomised intervention studies. Health Technol Assess. 2003;7:iii-x, 1-173.

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