Table 1.

Classification of the literature consulted, according to strength of evidence

Level of evidence for studies on intervention:
A1	systematic reviews that comprise at least several A2 quality trials whose results are consistent
A2	high-quality randomized comparative clinical trials (randomized, double-blind controlled trials) of sufficient size and consistency
B	randomized clinical trials of moderate quality or insufficient size, or other comparative trials (non-randomized, comparative cohort study, patient control study)
C	non-comparative trials
D	opinions of experts, such as project group members
Level of evidence for conclusions:
1	at least one systematic review (A1) or two independent grade A2 studies
2	at least two independent grade B studies
3	at least one grade A2, B or C study
4	opinions of experts, such as project group members