Paper selection

The stage 1 search results were imported into the bibliographical software management package EndNote V.X8.2 and assessed. The stage 2 results were imported into the same EndNote library and results were deduplicated. Stage 2 results remaining after deduplication were assessed. An extensive screening process was undertaken. At the first stage, two independent reviewers (ARo, SL) screened record titles and abstracts for relevance against the screening criteria. Abstracts were double screened (MM) where there were any doubts about eligibility. Full-text papers were screened in pairs (ARo, JT) (MM, SL); both reviewers in each pair independently screened studies for eligibility. A third reviewer resolved eligibility disagreements. Grey literature was reviewed and discussed within the team to agree relevance.