Exclusion criteria
Studies fulfilling the following criteria will be excluded:
Each study will be screened by two reviewers independently based on the title and abstract according to the inclusion and exclusion criteria (described below). If there are any discrepancies between the reviewers, a third reviewer will adjudicate. When the studies have been selected, the full texts will be reviewed to confirm they meet the inclusion criteria. Data will be extracted from these studies and the quality will be assessed for risk of bias and applicability. Studies which satisfy the inclusion criteria but are not in English will be translated prior to data extraction and quality assessment.