Systematic Reviews - a quick guide: Bias

As part of a systematic review a risk of bias analysis should be carried out for all included studies.

There are a number of different types of bias including the following which can affect the quality of a study. The following are the main types of bias in relation to randomised controlled trials:

Selection bias

Performance bias

Detection bias

Reporting bias

For an explanation of these and other different kinds of bias and the consequences of such bias please refer to the resources below:

Cochrane Collaboration    Assessing the risk of bias in included studies

Chapter 8 of the Cochrane Handbook

Australian Government National Health and Medical Research Council Assessing the risk of bias: Draft module - This contains a useful list of different tools to assess the risk of bias for different types of studies