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Evidence-Based Research (EBR): Types of Questions/Studies

Levels of Evidence

As you move up the pyramid, the study designs are more rigorous.

For definitions of the various study designs, see the Glossary (PDF) provided by the University of Arizona College of Pharmacy. 

Study designs pyramid

The Evidence-Based Pyramid is divided into levels. Each ascending level represents a different type of study design and corresponds to increasing rigor, quality, and reliability of the evidence. The levels from the bottom to the top are: background information; case-controlled studies; cohort studies; randomized controlled trials; critically-appraised topics; and, lastly, the highest quality of evidence, systematic reviews.

EBM Pyramid and EBM Page Generator. (c) Copyright 2006-2011. Trustees of Dartmouth College and Yale University. All Rights Reserved. Produced by Jan Glover, David Izzo, Karen Odato and Lei Wang.

Qualitative/Quantitative Research

Types of Questions

Common Question Types:

  • Therapy: Questions about the effectiveness of interventions in improving outcomes in sick patients / patients suffering from some condition. 
    • Example: Is Tamiflu more effective than over-the-counter medications in shortening the recovery period from the flu? 
    • Ideal types of studies: Randomized Controlled Trial
  • Prevention: Questions about the effectiveness of an intervention or exposure in preventing morbidity and mortality. 
    • Example: Are pressure-reducing mattresses more effective than patient repositioning in preventing pressure ulcers amongst elderly nursing home residents? 
    • Ideal types of studies: Randomized Controlled Trial; Cohort Study; Case Control
  • Diagnosis: Questions about the ability of a test or procedure to differentiate between those with and without a condition or disease. 
    • Example: Is ultrasound more effective than mammogram in detecting breast cancer in symptomatic younger women? 
    • Ideal types of studies: Prospective, blind controlled trial comparison to gold standard
  • Prognosis: Questions about the probable cause of a patient's disease or the likelihood that he or she will develop an illness. 
    • Example: Do premature babies have an increased risk of developing asthma as adolescents? 
    • Ideal types of studies: Cohort Study; Case Control; Case Series/Case Report
  • Etiology/Harm: Questions about the harmful effect of an intervention or exposure on a patient. 
    • Example: Are male adolescents who consume energy drinks more prone to migraines than male adolescents who do not consume energy drinks? 
    • Ideal types of studies: Randomized Controlled Trial; Cohort Study; Case Control