Table 2 Definition of level of evidence

From: Summary of the Standards, Options and Recommendations for the management of patients with nonmetastatic prostate cancer (2001)

Level A

There exists a high-standard meta-analysis or several high-standard randomised clinical trials that give consistent results

Level B

There exist good quality evidence from randomised trials (BI) or prospective or retrospective studies (B2). The results are consistent when considered together

Level C

The methodology of the available studies is weak or their results are not consistent when considered together

Level D

Either the scientific data do not exist or there is only a series of cases

Expert agreement

The data do not exist for the method concerned, but the experts are unanimous in their judgement

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