Study Selection
Two reviewers will screen all the titles and/or abstracts independently and if a disagreement is reached on whether a study should be included in the full-text eligibility assessment; appropriate discussion between the two reviewers will follow, and if disagreement persists then a third independent reviewer will be invited to reach a consensus. The eligibility of each full-text study to be included in the systematic review according to the aforementioned characteristics will be assessed independently by the two reviewers and any disagreement will be solved by the independent third reviewer to reach consensus. All the required information for this systematic review was found in the studies. A summary of the selection process according to PRISMA guidelines for systematic reviews is presented in Figure 1. Initially the search retrieved 984 studies, from which 242 duplicates were removed resulting in 742 studies. From the remaining abstracts and/or titles 706 records were excluded according to eligibility criteria, a further 32 from the 36 full-text reviews were excluded based on not matching inclusion/exclusion criteria. Four studies remained at the end of the selection process.