RESULTS
A total of 21,884 articles were identified by the search, of which 520
were eligible for full text review (Figure 1) and a further 11 were
identified from bibliographic searches. Of these, 18 studies were
included in the review, and seven were included in the meta-analysis.
The reasons for excluding 513 papers are detailed in figure 1. The
quality assessment showed that no studies were of low quality.