Bias in Medical/Clinical Research

Learning from clinical experience (whether during formal research or in the course of patient care) is impeded by mainly two processes: bias and chance. Medical research results many times become inconclusive because some bias is detected after the results are available. A dictionary definition of ‘bias’ is ‘a onesided inclination of the mind. In statistics, ‘bias’ is ‘systematic error’ that can produce results that depart from the true values. That is, bias is a process at any stage of inference tending to produce results that depart systematically from the true values. It is any trend in the design, collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth. Therefore, it is important that all sources of bias are considered at the time of planning a study, and all efforts are made to control them. Other type of error is ‘random error’. Random variation can never be eliminated totally; however, one can reduce the role of chance by proper design, adequate sample size, and appropriate analyses. Chance should always be considered when assessing the results of clinical observations. But it is very important to note that these two sources of error–bias and chance–are not mutually exclusive. In clinical research a great deal of effort is aimed at avoiding bias whenever possible and controlling for and estimating its effects when bias is unavoidable. On the other hand, random error resulting from the play of chance is inherent in all observations. Though it can be minimized, it cannot be avoided altogether.