Venue: Egyptian Medical Syndicate (Dar El-Hekma), Downtown, Cairo

Date and Time: Friday January 27, 2012. At 2:00 pm

Tutor: A F Nabhan

Overview

A bias is a systematic error, or deviation from the truth, in results or inferences. Biases can operate in either direction: different biases can lead to underestimation or overestimation of the true intervention effect. Biases can vary in magnitude: some are small (and trivial compared with the observed effect) and some are substantial (so that an apparent finding may be entirely due to bias). Even a particular source of bias may vary in direction: bias due to a particular design flaw (e.g. lack of allocation concealment) may lead to underestimation of an effect in one study but overestimation in another study. It is usually impossible to know to what extent biases have affected the results of a particular study, although there is good empirical evidence that particular flaws in the design, conduct and analysis of randomized clinical trials lead to bias. Because the results of a study may in fact be unbiased despite a methodological flaw, it is more appropriate to consider risk of bias.