Table 2. Definition of level of evidence.

Level A

There exist a high-standard meta-analysis or several high-standard randomised clinical trial which give consistent results

Level B

There exist clinical trials (therapeutic trials, quasiexperimental trials or comparisons of populations) for which the results are consistent when considered together

Level C

There exist clinical trails (therapeutic trials, quasiexperimental trails, or comparisons of populations) for which the 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