Below is an example of an evidence pyramid, or the hierarchy of study design. It can be looked at as a way of thinking about what makes up medical literature. The answers to the question asked may not always be found in the highest level of study. In the absence of the best evidence, consider moving down the pyramid to other types of studies. Study design details.
Howard White, CEO of The Campbell Collaboration, blogged about a knowledge brokering platform pyramid. Below is a way of thinking about groupings of rigorous evidence that get translated into policy and practice. In the pyramid, each level is more heavily brokered.
Keep study design in mind when searching the literature. Below is a chart of the best type of study to look for based on your question type:
Question Type |
Best Study Designs (in order of quality) |
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Therapy - select treatments for patients that do more good than harm & are worth the effort and cost of using |
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Diagnosis - select and interpret diagnostic tests, in order to confirm or exclude a diagnosis, based on considering specificity, sensitivity, likelihood ratios, expense, safety, etc. |
Prospective, blind comparison to a gold standard |
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Etiology - id causes for disease (including iatrogenic forms) |
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Prognosis - estimate the patient's likely clinical course over time and anticipate likely complications |
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Prevention - reduce the chance of disease by determining/modifying risk factors, early diagnosis by screening |
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Clinical Exam |
Prospective, blind comparison to a gold standard |
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Cost - compare costs and consequences of different treatments/tests |
Economic Analysis |
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Questions of therapy, etiology, and prevention that can best be answered by an RCT can also be answered by a meta-analysis or systematic review. Etiology and harm studies can be answered by an RCT if the ethical issues of the study will allow it. |
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