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Evidence-Based Practice: Study Design

Hierarchy of Evidence-Based Information for Clinical Questions

Study design

The type of question may determine the type of study needed.

Question Type       Best Study Type

Diagnosis                prospective,
                                  blind comparison to gold standard

Therapy                   RCT> cohort> case control> case series

Etiology/Harm         RCT> cohort> case control> case series

Prognosis                Cohort> case control> case series

Prevention               RCT> cohort> case control> case series

Evidence Grading Systems

GRADE - The Grading of Recommendations Assessment, Development and Evaluation (short GRADE) Working Group began in the year 2000 as an informal collaboration of people with an interest in addressing the shortcomings of present grading systems in health care. The working group has developed a common, sensible and transparent approach to grading quality of evidence and strength of recommendations. Many international organizations have provided input into the development of the approach and have started using it

US Preventive Services Task Force - USPSTF assigns 5 letter grades (A,B,C,D,and I)

UK National Health Service - developed in conjunction with the Oxford Centre for Evidence-based Medicine

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