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Table 2 Hierarchy of evidence [18]

From: The Prevalence of low back pain in Africa: a systematic review

Level 1 Meta-analysis of randomized controlled clinical trials
Level 2a One randomized controlled clinical trial (RCT)
Level 2b One non-randomized, or non-controlled, or non-blinded clinical trial
Level 3 Observational studies
Level 4 Pre-post test clinical trials
Level 5 Descriptive studies
Level 6 Anecdotal evidence