What is bias?

Bias is a systematic error in the design, administration, or analysis of a study. Because of bias, study results deviate from their true value and researchers draw erroneous conclusions.

There are several types of bias, and different research designs or fields are susceptible to different types of research bias. For example, in health research, bias arises from two main sources:

• The approach adopted for selecting study participants
• The approach adopted for collecting or measuring data

These are, respectively, selection bias and information bias.