3. Factors that may decrease the quality level of a body of evidence.

1. Limitations in the design and implementation of available studies suggesting high likelihood of bias.

2. Indirectness of evidence (indirect population, intervention, control, outcomes).

3. Unexplained heterogeneity or inconsistency of results (including problems with subgroup analyses).

4. Imprecision of results (wide confidence intervals).

5. High probability of publication bias.