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Evidence Based Dentistry
Hierarchy of evidence for clinical questions related to therapy, prevention, etiology or harm.
Always start an EBD search looking for the highest level of evidence. If a meta-analysis is not available on the topic, look next for systematic reviews without statistical synthesis, next for randomized control trials, next for cohort studies, next for case control studies, etc.
For more detailed information about the levels of evidence see the Oxford Centre for Evidence-based Medicine - Levels of Evidence (March 2009).
Definitions of Study Types
"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.Meta-analysis: an introduction into a research process. Special Care in Dentistry 28, no. 4 (2008):125-30. UNC-CH Full Text
"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 SE, Matthews DC. A guide to systematic reviews. Journal of the American Dental Association 135, no.6 (2004):747-53. Free Full Text
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. UNC-CH Full Text
"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. UNC-CH Full Text
"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. UNC-CH Full Text