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Bias

Bias

Per the Cochrane Handbook: "Review authors should seek to minimize bias" and they define bias as "a systematic error, or deviation from the truth, in results" (I. Boutron et al., 2023).

For more information on bias:

Types of bias can include:

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

Reducing Bias

Methods for reducing bias and error (Littell et al, n.d.):

  • 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

References

Boutron I, Page MJ, Higgins JPT, Altman DG, Lundh A, Hróbjartsson A. Chapter 7: Considering bias and conflicts of interest among the included studies. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.4 (updated August 2023). Cochrane, 2023. Available from www.training.cochrane.org/handbook.

Institute of Medicine. (2011). Finding what works in health care: Standards for systematic reviews. The National Academies Press. https://doi.org/10.17226/13059.

Littell, J., Valentine, J., & Young, S. (n.d.) Systematic reviews and meta-analysis: A Campbell Collaboration online course [Mooc].  Open Learning Initiative. https://oli.cmu.edu/courses/systematic-reviews-and-meta-analysis-o-f/