Table 1.

Hierarchy of evidence for therapeutic decisions

	Study design	Description
	Systematic reviews of randomized trials	A systematic approach in which results of several RCTs are critically assessed and evaluated. Results may be pooled to arrive at single estimate of treatment effect
	Randomized controlled trial	A trial in which participants are randomly allocated to treatment or control interventions and prospectively followed to assess outcomes of interest
	Systematic reviews	A systematic approach in which results of several observational studies are critically assessed and evaluated. Results may be pooled to arrive at single estimate of treatment effect
	Observational studies	A study where physician or patient preference determines allocation to treatment or control intervention. Such studies do not employ the process of randomization
	Unsystematic clinical observations	A study in which a cohort of patients receive an intervention without a control group for comparison

Adapted from: Guyatt GH, Haynes RB, Jaeschke R, Cook D, Greenhalgh T, Meade M, et al.²