Table 1.

Levels of evidence applied to studies included in this review

Strength of evidence	Criteria	Number of studies
Level 1	Strong evidence from at least one systematic review, meta-analysis, or integrated analysis	3
Level 2	Evidence from randomized controlled trials	7*
Level 3	Evidence from nonrandomized well designed trials, single-group pre/post intervention, cohort, time series, or matched-case control studies	1
Level 4	Evidence from well designed, nonexperimental, observational studies from more than one center or research group	0
Level 5	Opinions of respected authorities, based on clinical experience, descriptive studies, and reports of expert committees	0

^*Note: Two trials of identical design are only available as an integrated analysis16 and are included in the level 1 category.

Adapted from Clark and Mucklow.42