Skip to Main Content

Levels of Evidence and Study Design: Study Design by Question Type

Information on study design and levels of evidence to help you evaluate the medical, nursing and health care literature

Suggested Study Designs by Question Type

Etiology

Focus: Ailment causation

Study Design: Meta-Analysis/Systematic Eeview of randomized control trials (strongest), Systematic Review of cohort studies, Randomized Control Trials, Cohort Study, Case-Control, Case Series (weakest)

Diagnosis

Focus: Reliability of diagnostic measure against the "gold standard" diagnostic measure for the same ailment

Study Design: Meta-Analysis/Systematic Review of Cross Sectional Studies with consistent reference standards (strongest), Cross Sectional Studies with consistent reference standards, Studies without consistent reference standards, Case-Control or Case Series or Cohort Study of poor quality (weakest)

Prevention

Focus: Reduction of risk factors by disease identification

Study Design: Meta-Analysis/Systematic Review of Randomized Control Trials (strongest), Systematic Review of Cohort Studies, Randomized Control Trials, Cohort Study, Case-Control, Case Series (weakest)

Prognosis

Focus: Patient's clinical course over time

Study Design: Meta-Analysis/Systematic Review of Cohort Studies (strongest), Cohort Study (at/near ailment inception), Randomized Control Trials or Cohort Study, Case-Control or Case Series (weakest)

Therapy

Focus: Effect of intervention on patient

Study Design: Meta-Analysis/Systematic Review of Randomized Control Trials (strongest), Systematic Review of Cohort Studies, Randomized Control Trials, Cohort Study, Case-Control, Case Series (weakest)

References

  • Forrest, J. L., Miller, S. A., Miller, G. W., Elangovan, S., & Newman, M. G. (2019). Evidence-based decision making. In Newman, Michael G., Takei, Henry H., Klokkevold, Perry R., & Carranza, Fermin A. (Eds.), Newman and carranza's clinical periodontology (Thirteenth ed., pp. 1-9.e1). Elsevier. https://doi.org/10.1016/B978-0-323-52300-4.00001-1

  • OCEBM Levels of Evidence Working Group. (n.d.). CEBM Levels of Evidence Table. (Version 2) [Table]. Oxford Centre for Evidence-Based Medicine. Retrieved October 1, 2021.