The initial search identified 599 records; from these, 15 full-text
papers were identified for further examination. The other studies
were excluded on the basis of their abstracts because they did not
meet the inclusion criteria, were not relevant to the question under
study or were a duplicate report (see Figure 1 for the amended
PRISMA (Preferred Reporting Items for Systematic Reviews and
Meta-Analyses) flow chart). After screening the full text of the selected
papers, 10 studies (12 papers) met the inclusion criteria. All
studies were published in English. Additional data and clarification
of methodological issues were sought from the authors of all
studies. Two review authors responded to these requests