Reducing Bias

Types of bias can include:

• Publication, time lag, or multiple publication bias
• Location bias
• Citation bias
• Language bias
• Outcome reporting bias.

For more information on bias, see Cochrane Handbook Chapter 7: Considering Bias and Conflicts of Interest Among the Included Studies.

Methods for reducing bias and error:

• Develop and publish a protocol before beginning the review
• Create explicitly eligibility criteria
• Use a variety of search terms and databases to find studies potentially eligible for inclusion
• Search for grey literature
• Request missing data from primary study authors
• Use structured screening, data extraction, and coding forms
• Conduct screening, extraction, and coding in duplicate and resolve discrepancies
• Assess risk of bias including risks of publication bias and reporting bias
• Use meta-analysis if possible (if 2 or more studies provide quantitative data on parallel constructs)
• Document methods and decisions in sufficient detail for replication

Source: Systematic Reviews & Meta-Analysis - The Campbell Collaboration and the Open Learning Initiative

• Quality Assessment/Risk of Bias Tools