Quality appraisal
The CASP (critical appraisal skills programme, 2006) framework was used and adapted to appraise the quality of
the research. However, relevance to the study rather than any clinical service or organisation was a minor but necessary adaptation of the framework. The key questions asked when reviewing the studies are included in Table 2. The studies were initially reviewed by one author (LRC). Subsequently peer scrutiny of study reviews and the overall
methodological or quality issues across the body of literature,took place in regular meetings.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.