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Systematic Reviews: National Databases and Bias

National Databases

African Index Medicus Database - The world Health Organization, in collaboration with the Association for Health Information and Libraries in Africa (AHILA) produces this index to African health literature and information sources.

CAJ: China Academic Journal - Full text access to journal articles published in China in all subject areas.

LILACS - An important and comprehensive index of scientific and technical literature of Latin America and the Caribbean.




Bias may result from systematic errors in the research methodology.

Common types of bias:

Selection 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. 

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 nonsignificant 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