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Evidence Based Dentistry: Levels of Evidence

Definitions of Study Types - Primary Sources/Unfiltered Information

Randomized Controlled Trial (RCT) - "Randomised controlled trials (RCT), or randomised clinical trials, are experimental studies where the effect of an intervention is assessed by collecting data before and after an intervention has taken place. RCT are used to compare an intervention with one or more other interventions or with no intervention."
Levin, K. A. Study design VII: Randomised controlled trials. Evidence-based dentistry 8, no. 1 (2007):22-3. ECU Libraries Full Text

Cohort Study - "A cohort study is one in which a group of subjects, selected to represent the population of interest, is studied over time."
Levin, K. A. Study design IV: Cohort studies. Evidence-based dentistry 7, no. 2 (2006):51-52. ECU Libraries Full Text

Case-Control Study - "Like cohort studies, the purpose of case-control studies is to establish association between exposure to risk factors and disease. Unlike cohort studies, however, members of the population with the disease are selected into the study at the outset and risk factor information is collected retrospectively"
Levin, K. A. Study design V: Case-control studies. Evidence-based dentistry 7, no. 3 (2006):83-84. ECU Libraries Full Text

Cross-Sectional Study -  Levin, K. A. Study design III: Cross-sectional studies. Evidence-based dentistry 7, no. 1 (2006):24-25. ECU Libraries Full Text

Meta-Analysis & Systematic Reviews - Secondary Sources/Filtered Information

Filtered Information/Secondary Sources

Meta-analysis - Thoroughly examines a number of valid studies on a topic and combines the results using accepted statistical methodology as if they were from one large study.
"Meta-analysis is a tool by which small, related studies are identified and, through systematic review, are combined into a common data pool for a single, larger population analysis."
Livingston M,et al. (2008). Meta-analysis: An introduction into a research process. Special Care in Dentistry, 28(4), 125-30. ECU Libraries Full Text

Systematic Reviews - Focuses on a clinical topic and answers a specific question. An extensive literature search is conducted to identify all studies with sound methodology. The studies are reviewed, assessed, and the results summarized according to the predetermined criteria of the review question.

"Systematic reviews are summaries of the world literature on a specific topic that use explicit methods to systematically search, critically appraise and synthesize the evidence from clinical research."
Sutherland S. E., Matthews D. C. (2004). A guide to systematic reviews. Journal of the American Dental Association, 135(6), 747-53. ECU Libraries Full Text
 

From: http://www.hsl.unc.edu/services/tutorials/EBM/Supplements/QuestionSupplement.htm

Hierarchy of Evidence