The remaining 26 studies were included since they were
deemed to be sufficiently rigorous, credible and relevant to
include for full review. Some issues were identified during
the quality appraisal (see Table 3). Whilst these issues were
not sufficient to exclude the studies they did demonstrate
the great diversity in designs as well as being important
considerations when interpreting the overall synthesis in
this review. An overview of key methodological issues is
presented in Table 3. The issues are cross-referenced to
individual studies summarised in Table 4.