| Evidence Direct: Type of studies
The following all come under the category of evidence-based' resources.
Systematic Review is a literature review focused on a single question which tries to identify, appraise, select and synthesis all high quality research evidence relevant to that question. Systematic reviews use explicit methods to identify, select, and critically evaluate relevant research. Some systematic reviews also include a meta analysis. The Cochrane Centre produces high-quality systematic reviews. You can also find systematic reviews in PubMed Clinical Queries.
Meta-analysis is a systematic review that combines the results of several studies using quantitative statistics. (Some statisticians rank this as above the level of Systematic Review).
Randomised controlled trials – use of a control with subjects randomly selected to join either a control or an experimental group, with a comparison made at the end of the study. An RCT is considered the ‘gold standard’.
Guidelines are based on systematic reviewing techniques. Guidelines involve consultation with patients and subject specialists and can be adapted to meet local needs.
Case-control studies – patients with the same condition are matched with controls.
Case reports – single cases reviewed.
Cohort studies – groups treated differently, then followed up after many years.
Cross-sectional surveys – data collected on one occasion only across a single population.
Evidence summaries are resources (such as UpToDate, Clinical Knowledge and Clinical Evidence) that offer summaries of evidence-based information on a topic.
Narrative Reviews are opinion pieces pretending to be systematic reviews: they review the literature, but not systematically. Their use is limited.
See also: National Library of Medicine (USA) Guide to Study Types.