Table 1.

Level of evidence and grade of recommendation in the Korean clinical practice guideline for aneurysmal subarachnoid hemorrhage

Level of evidence (LOE)
Ia	Meta-analysis of randomized controlled trials
Ib	At least one randomized controlled trial
IIa	At least one well-designed controlled study without randomization
IIb	At least one other type of well-designed quasi-experimental study
III	Descriptive studies such as comparative studies, correlation studies and case studies
IV	Expert committee reports, clinical experiences and opinions of respected authorities
Grade of recommendation
A (LOE Ia and Ib)	Recommendation should be followed
B (LOE IIa, IIb, and III)	Recommendation being reasonable or recommended to do
C (LOE IV)	Recommendation being considered to do
Good clinical practice (GCP)	Consensus opinion of the guideline development group