Table 1 Evidence level (EL) (from 84).*

Level	Evidence
* The first version of this guideline was compiled in 2003 and published in 2004, in other words, prior to the development of the DELBI and AWMF criteria for defining the level of evidence. The level of evidence was determined in analogy to the evaluation of guidelines issued by foreign professional associations (s. above) and this form of assessment was retained in the revised version of the guidelines.
I a	Systematic review with meta-analysis of randomized controlled studies
I b	At least one randomized controlled trial
II a	At least one well-designed controlled study without randomization
II b	At least one other type of well-designed quasi-experimental study
III	Well-designed non-experimental descriptive study, e.g. comparative, correlation and case studies
IV	Expert committee reports or opinions and/or clinical experiences of respected authorities