*2.4. Selection of Studies*

After completing the search in each database, all references were imported into EndNote (=bibliographic software program) and then exported to Rayyan (=bibliographic software program designed to facilitate systematic reference selection), in which the study selection was conducted. The study selection included the screening of titles, abstract and full-texts and conducting a forward and backward search. The search and study selection were conducted in January 2019 by two researchers independently from each other (YV and EVDL). Any doubts or disagreements between the two researchers were discussed with a third researcher (TD). The followed methodology was reviewed and approved by the head of the university library (KA). When important information in the articles was missing, authors were contacted via e-mail.
