Bias may result from systematic errors in the research methodology.
Common types of bias:
- Only choose studies which they are familiar with or support their view-point
- Occurs when the two groups being compared differ systematically, eg. differences in the characteristics between those who are selected for a study.
Performance bias - differences between groups in the care that is provided, or in exposure to factors other than the interventions of interest.
Detection bias - differences between groups in how outcomes are determined.
Attrition bias - differences between groups in withdrawals from a study.
Reporting bias - differences between reported and unreported findings.
Publication bias - Only select studies which have been published. In general, studies with statistically significant or positive results are more likely to be published than those with non-significant or negative results.(1)
Language bias - Only select studies written in English
Indexing bias - Only search a limited number of databases or use a limited choice of search terms.
1. Song F, Parekh S, Hooper L, et al. Dissemination and publication of research findings: an updated review of related biases. Health Technol Assess. 2010;14(8):iii, ix–xi, 1–193. doi: 10.3310/hta14080