Data extraction
All titles were screened by one reviewer (JW) and potentially-relevant titles were retained. Two reviewers (JW, RH) independently screened shortlisted abstracts, with any conflicts resolved by team discussion. Full texts were obtained for these titles, and a final decision on inclusion or exclusion was made for each of these titles following full text review against the eligibility criteria. Data extracted from studies selected for inclusion were first author, publication year, country, study objective, sample, methods, key study findings and links to efficiency improvement.