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Bias in Research Studies¹

¹ From Harvard Vanguard Medical Associates, Boston, Mass. Received June 23, 2004; revision requested August 11; revision received August 22; final version accepted January 21, 2005; updated August 29. Address correspondence to the author, Department of Radiology, Woodhull Medical Center, 760 Broadway, Brooklyn, NY 11026 (e-mail: gsica{at}sprynet.com).

Bias is a form of systematic error that can affect scientific investigations and distort the measurement process. A biased study loses validity in relation to the degree of the bias. While some study designs are more prone to bias, its presence is universal. It is difficult or even impossible to completely eliminate bias. In the process of attempting to do so, new bias may be introduced or a study may be rendered less generalizable. Therefore, the goals are to minimize bias and for both investigators and readers to comprehend its residual effects, limiting misinterpretation and misuse of data. Numerous forms of bias have been described, and the terminology can be confusing, overlapping, and specific to a medical specialty. Much of the terminology is drawn from the epidemiology literature and may not be common parlance for radiologists. In this review, various types of bias are discussed, with emphasis on the radiology literature, and common study designs in which bias occurs are presented.

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