Received September 09, 2009
Accepted September 13, 2009

Bias or bias is the systematic introduction of error into a sample or test by selecting or encouraging one result or response over others. Another view of the topic describes a deviation from the expected statistical value estimate from the amount that the test estimated. Or even a group of people or things containing more species than usual, therefore not giving fair or accurate results. It is a term that refers to how far the statistical mean is from the parameter that the statistical test is estimating. It is the error that arises when estimating. Internationally known as bias, it is a term used to describe differences between what is found in research and the truth. “Any effect at any stage of investigation or inference tending to produce results systematically different from true values ​​(to distinguish from random error)” One can cite as an example of bias: healthy selection bias, compliance bias, surveillance or supervision bias, survival bias or natural selection. The double-blind randomized clinical trial in intervention studies is a good example of an attempt to reduce bias.