Other examples of evidence hierarchies
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Evidence hierarchy: Other examples

United States Preventive Services Task Force

In the world of medicine the United States Preventative Services Task Force is committed to evidence-based medical practice. The job of the Task Force is to review a range of clinical preventive health care services and then develop recommendations for care clinician and health systems. To ensure its recommendations are based on robust and reliable evidence it has created its own evidence hierarchy.

I: Properly powered and conducted randomised controlled trial (RCT); well-conducted systematic review or meta-analysis of homogeneous RCTs

II-1: Well-designed controlled trial without randomisation

II-2: Well-designed cohort or case-control analytic study

II-3: Multiple time series with or without the intervention; dramatic results from uncontrolled experiments

III: Opinions of respected authorities

Like the Centre for Education Statistics and Evaluation, the Task Force recognises the benefits of randomised controlled trials. Its procedural manual states "although RCTs cannot answer all key questions, they are ideal for questions of the benefits or harms of various interventions".


Scottish Intercollegiate Guidelines Network

Another hierarchy of evidence used in the healthcare industry can be found on the Scottish Intercollegiate Guidelines Network (SIGN) website. SIGN was established in 1993 to develop evidence-based clinical guidelines for the National Health Service in Scotland.

1++ High quality meta-analyses, systematic reviews of randomised controlled trials (RCTs), or RCTs with a very low risk of bias

1+ Well conducted meta-analyses, systematic reviews of RCTs, or RCTs with a low risk of bias

1 - Meta-analyses, systematic reviews of RCTs, or RCTs with a high risk of bias

2++ High quality systematic reviews of case-control or cohort studies; high quality case-control or cohort studies with a very low risk of confounding or bias and a high probability that the relationship is causal

2+ Well conducted case-control or cohort studies with a low risk of confounding or bias and a moderate probability that the relationship is causal

2 - Case-control or cohort studies with a high risk of confounding or bias and a significant risk that the relationship is not causal

3 Non-analytic studies, e.g. case reports, case series

4 Expert opinion


An evidence hierarchy for Australian social policy makers

It is harder to find evidence hierarchies in an education setting, or an Australian setting. However, economist Andrew Leigh suggests the following hierarchy for Australian policy makers:

1. Systematic reviews (meta-analyses) of multiple randomised trials

2. High quality randomised trials

3. Systematic reviews (meta-analyses) of natural experiments and before-after studies

4. Natural experiments (quasi-experiments) using techniques such as differences-in-differences, regression discontinuity, matching, or multiple regression

5. Before-after (pre-post) studies

6. Expert opinion and theoretical conjecture