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Table 1 Hierarchy of evidence (Lloyd-Smith 1997)

From: The postural effects of load carriage on young people – a systematic review

Level of evidence Study design
1a Meta-analysis of randomised controlled trials
1b One individual randomised controlled study
2a One well-designed, non randomised controlled study
2b Well – designed quasi-experimental study
3 Non-experimental descriptive studies-comparative/ case studies
4 Respectable opinion