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Table 2 Types of Studies by Evidence Level

From: Evidence for the use of complementary and alternative medicines during fertility treatment: a scoping review

Level of Evidence Types of Studies
Level I systematic review of level II studies, meta-analysis
Level II randomized control trial
Level III-1 pseudorandomized control trial
Level III-2 comparative studies including non-randomized experimental trials, cohort studies, case-control studies, interrupted time series with controls
Level III-3 comparative studies without controls including historical control studies, two or more single-arm studies, interrupted time series without a parallel control group, cross-sectional
Level IV case series, nonsystematic review, survey, qualitative interviews