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Table 1 Levels of evidence

From: How to review a case report

Level of evidence

Type of evidence

1a

Evidence obtained from meta-analysis of randomized trials

1b

Evidence obtained from at least one randomized trial

2a

Evidence obtained from one well-designed controlled study without randomization

2b

Evidence obtained from at least one other type of well-designed quasi-experimental study

3

Evidence obtained from well-designed non-experimental studies, such as comparative studies, correlation studies, and case reports

4

Evidence obtained from expert committee reports or opinions or clinical experience of respected authorities

  1. Produced by Bob Phillips, Chris Ball, Dave Sackett, Doug Badenoch, Sharon Straus, Brian Haynes, Martin Dawes since November 1998. Updated by Jeremy Howick March 2009. Assessed from: http://www.cebm.net/oxford-centre-evidence-based-medicine-levels-evidence-march-2009. Assessed on 1 Nov 2015