Hierarchy of evidence
Encyclopedia
Evidence hierarchies reflect the relative authority of various types of biomedical research
. Although there is no single, universally-accepted hierarchy of evidence, there is broad agreement on the relative strength of the principal types of research. Randomized controlled trials (RCTs) rank above observational studies, while expert opinion and anecdotal experience are ranked at the bottom. Some evidence hierarchies place systematic review
and meta analysis above RCTs, since these often combine data from multiple RCTs, and possibly from other study types as well. Evidence hierarchies are integral to evidence-based medicine
.
The use of evidence hierarchies has been criticized as allowing RCTs too much authority. Not all research questions can be answered through RCTs, either because of practical issues or because of ethical issues. Moreover, even when evidence is available from high-quality RCTs, evidence from other study types may still be relevant.
Greenhalgh suggests that: "The hierarchy of evidence
Standard notation for the relative weight carried by the different types of primary study when making decisions about clinical interventions (the “hierarchy of evidence”) puts them in the following order*:
1.Systematic reviews and meta-analyses
2.Randomised controlled trials with definitive results (confidence intervals that do not overlap the threshold clinically significant effect)
3.Randomised controlled trials with non-definitive results (a point estimate that suggests a clinically significant effect but with confidence intervals overlapping the threshold for this effect)
4.Cohort studies
5.Case-control studies
6.Cross sectional surveys
7.Case reports."
(Greenhalgh, T. 1997. p244.)
Note that she refers* to Guyatt et al 1995.
Greenhalgh 1997 http://www.bmj.com/content/315/7102/243.extract
Biomedical research
Biomedical research , in general simply known as medical research, is the basic research, applied research, or translational research conducted to aid and support the body of knowledge in the field of medicine...
. Although there is no single, universally-accepted hierarchy of evidence, there is broad agreement on the relative strength of the principal types of research. Randomized controlled trials (RCTs) rank above observational studies, while expert opinion and anecdotal experience are ranked at the bottom. Some evidence hierarchies place systematic review
Systematic review
A systematic review is a literature review focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. Systematic reviews of high-quality randomized controlled trials are crucial to evidence-based medicine...
and meta analysis above RCTs, since these often combine data from multiple RCTs, and possibly from other study types as well. Evidence hierarchies are integral to evidence-based medicine
Evidence-based medicine
Evidence-based medicine or evidence-based practice aims to apply the best available evidence gained from the scientific method to clinical decision making. It seeks to assess the strength of evidence of the risks and benefits of treatments and diagnostic tests...
.
The use of evidence hierarchies has been criticized as allowing RCTs too much authority. Not all research questions can be answered through RCTs, either because of practical issues or because of ethical issues. Moreover, even when evidence is available from high-quality RCTs, evidence from other study types may still be relevant.
Greenhalgh suggests that: "The hierarchy of evidence
Standard notation for the relative weight carried by the different types of primary study when making decisions about clinical interventions (the “hierarchy of evidence”) puts them in the following order*:
1.Systematic reviews and meta-analyses
2.Randomised controlled trials with definitive results (confidence intervals that do not overlap the threshold clinically significant effect)
3.Randomised controlled trials with non-definitive results (a point estimate that suggests a clinically significant effect but with confidence intervals overlapping the threshold for this effect)
4.Cohort studies
5.Case-control studies
6.Cross sectional surveys
7.Case reports."
(Greenhalgh, T. 1997. p244.)
Note that she refers* to Guyatt et al 1995.
External links
School of Health and Related Research, University of Sheffield, "Hierarchy of evidence". http://www.shef.ac.uk/scharr/ir/units/systrev/hierarchy.htm. Accessed 2008-03-31.Greenhalgh 1997 http://www.bmj.com/content/315/7102/243.extract