Flow chart of the identification, screening and included articles. Figure illustrates the process used to search for studies that were included in the review. Studies were searched in the PubMed and Scopus databases. ‘Identification’ shows the number of articles retrieved using the search terms (403) and after removal of duplicates (334). ‘Screening’ shows the number of articles whose titles, abstracts and keywords were screened against the study inclusion and exclusion criteria (334) and the number of articles that were excluded at this stage (201). ‘Eligibility’ shows the number of full text articles that were screened against the inclusions and exclusion criteria (133) and the number of articles that were excluded at this stage (97). ‘Inclusion’ shows that number of articles that were included in the review (66), including those that met the inclusion criteria (36) and 30 articles identified from searching the reference lists of the 36 included articles.