Bias in case-control studies. A review.

It has been widely accepted that one reason for inconsistent or contradictory results of epidemiologic studies is bias. Therefore, an appreciation of potential sources of bias has become a critical issue in epidemiology. A large number of different sources and possible mechanisms of bias have been described but a consistent terminology has not evolved. Different authors have used different terms when referring to essentially the same type of bias. For example, Kleinbaum et al' and Rothinan2 classify biases into selection bias, information bias and confounding. Sackett offered a more detailed classification, with five major types of sampling bias (eg, admission rate bias, membership bias) and four types of measurement bias (eg, diagnostic suspicion bias, recall bias).3 Feinstein distinguishes, inter alia, among susceptibility bias, performance bias, transfer bias and detection bias.4 Last's Dictionary of epidemiology5 gives definitions of 26 biases but fails to mention many of the terms proposed by other authors.