Subject Guides: PICO: Form a Focused Clinical Question: 2. Align: Levels of Evidence

Align: Levels of Evidence

Evidence-Based Medicine: Resources by Levels of Evidence

Image: Bradley A. Long and Audrey Rock, Central Michigan University Libraries (©2016). Based on the EBM Page Generator from Dartmouth College and Yale University (©2006) and the Coursera MOOC “Understanding Clinical Research: Behind the Statistics” (©2016).

Study designs are placed into a hierarchy based on their reliability (probability of bias) known as the Levels of Evidence.

The Levels of Evidence are often represented by a pyramid, with the highest levels of evidence (least common) near the top, and the lowest levels of evidence (most common) near the bottom.

Types of Study Design:

Systematic Reviews & Meta-Analysis
Double-Blind & Randomized Controlled Trials
Cohort Studies
Case-Control Studies
Case Series & Case Reports

Introduction to Study Design
Defines types of study designs and explains what to look for when reading research to determine the study design. Source: Jeremy Howick, Centre for Evidence-Based Medicine (CEBM)
The Well-Built, Patient-Oriented Clinical Question
Use this worksheet to clarify the parts of your PICO question. Source: Dartmouth Biomedical Libraries

Question Type & Study Design

Some study designs are better suited to answer certain types of questions. Identifying the clinical domain your question falls under can help determine what study designs to look for in order to find the best, most suitable evidence. Systematic reviews and meta-analyses are always preferred.

Check off the clinical domain and preferred study design type on the Well-Built, Patient-Oriented Clinical Question worksheet. The link to that worksheet can be found above.

Clinical Domain	Preferred Study Design (after systematic reviews and meta-analyses)
Cost-Effectiveness	Economic Analysis
Diagnosis	Cross-Sectional Studies or Gold Standard
Etiology or Prognosis	Cohort > Case-Control > Case Series
Prevention	Randomized Controlled Trial > Controlled Trial > Cohort > Case-Control
Quality of Life	Qualitative Studies
Therapy	Randomized Controlled Trial > Controlled Trial or Quasi-Experimental Studies

For example:

Clinical question: In adult patients with total hip replacements, how effective is pain medication compared to aerobic stretching in controlling post operative pain during the perioperative and recovery time?

Clinical domain: Therapy

Preferred study designs: Systematic Reviews, Meta-Analyses, Randomized Controlled Trials, and Controlled Trials

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