Guidelines for Reporting Medical Research: A Critical Appraisal

Table 1

Hierarchy of evidence.

Study type	Level of evidence	Strength of recommendation
Systematic reviews and meta-analyses of randomized controlled trials	1a	A
Randomized controlled trials	1b
Nonrandomized controlled trials	2a	B
Cohort studies	2b
Case-control studies	3	C
Case studies, expert opinions	4	D
Diagnostic studies	—	—