Risk of bias evaluation in the included studiesĀ 
The risk of bias in these studies was evaluated using the STROBE guidelines.(21) (Appendix 2)
This guide is made up of 22 items which include questions about the design of information, participants, main variables, data registration, etc. having to answer yes or no to each one. Two statistic reviewers SC and MC evaluated the items in each article and in case of any disagreement, MP revised it and it was resolved by consensus.