LibGuides: Evidence-Based Practice: Study Design Hierarchy

Type of Question

Diagnosis Question:

Does this diagnostic test accurately distinguish between patients who do and do not have a specific disorder?1

Therapy Question:

What effect does an intervention have on particular patient groups? Does it do more good than harm? Determination of clinical and cost effectiveness.

Prognosis Question:

What is the probable clinical course of this patient over time? What main prognostic factor am I considering?³

Harm/Etiology Question:

Does this exposure/intervention cause a harmful effect on patients? What are the causes/risk factors for disease?2

Information adapted from the following sources:

1. Sackett, DL, et al. Evidence Based Medicine: How to Practice and Teach EBM. 2nd ed. Edinburgh: Churchill Livingstone, 2000. BHSL Call Number: WB 102 E933 2000

2. Tutorial: How To Form and Answerable Clinical Question. (2006) Cincinnati Children's.

3. NCI Dictionary of Cancer Terms

6S Hierarchy of Pre-Appraised Evidence

DiCenso, A., Bayley, L., & Haynes, R. B. (2009). Accessing pre-appraised evidence: fine-tuning the 5S model into a 6S model. Evidence based nursing,12(4), 99-101.

Type of Question Determines Type of Study

Select the best study type to answer your clinical question:

Type of Question	Best Study Type
Therapy	RCT > Cohort > Case Control > Case Series
Diagnosis	Prospective, Blind Comparison to Gold Standard
Prognosis	Cohort > Case Control > Case Series
Harm/Etiology	RCT > Cohort > Case Control > Case Series

Questions answered best by RCTs may also be answered by systematic reviews and meta-analyses