Appraising the evidence: what is selection bias?

• DOI: 10.1136/ebmh.10.3.67
• Publication Date: 2008-12-31T23:45:42Z
• Authors: Max Henderson; Lisa Page
• Keywords: Information bias; Value (mathematics)

Almost all studies are prone to error—they use samples drawn from a population estimate what is occurring or might occur in the whole population. These errors can broadly be divided into two: random error and systematic error. Random play of chance results an effect (for example, relative risk) being equally likely above below true value. Its role assessed with statistical measures such as p values confidence intervals. Systematic called bias, also leads further information which relates misclassification data, selection focus this article.

### Bias

Any trend collection, analysis, interpretation, publication review data that lead conclusions systematically different truth. (Last J. A dictionary epidemiology , 2001)

Bias limits analysis. It particularly problematic because, unlike confounding, little done “allow” “control” for it once have been collected. As many ways issue study design, planning practice.

Selection bias epidemiological occurs when there difference between characteristics those selected who not. intervention …