Fig. 1

Flow diagram of the review. From the 104 studies included in the database, 63 that provided statistical results were included in the narrative syntheses. The 34 studies relevant to the question #2 providing appropriate data were included in the meta-analyses. Twenty-six studies were included in both the meta-analyses and the narrative synthesis. Both the narrative syntheses and the meta-analyses constitute the systematic review. Therefore, the studies included in the database but which did not provide statistical results nor appropriate data for the meta-analyses were not included in the systematic review. *Literature screened on title and full text