Table 1.

Study designs and their levels of evidence

Study design	Level of evidence †
Meta‐analysis or systematic review (MA/SR)
High‐quality	1+
Satisfies all of the following 5 items: Low risk of bias Directness Precision Consistency among studies Publication bias free
Low‐quality	2
Otherwise
Randomized controlled trial (RCT)
High‐quality	1
Satisfies all of the following 3 items: Low risk of bias Directness Precision
Low‐quality	2
Otherwise
Prospective cohort study	2
Pre‐specified sub‐analysis of RCT	2
Retrospective cohort study	3
Case‐control study	3
Post hoc sub‐analysis of RCT	3
Single‐arm trial	3
Cross‐sectional study	3
Case series or case report	3

^†Level of evidence: 1+ (highest) to 3 (lowest).