Screening and Eligibility

The initial search yielded 1,841 search results in the database search, and a further 1,171 in the grey literature search. These numbers represent the total search results identified prior to any screening or removal of duplicates. All identified records from the database search were imported into EndNote X8^©. The database search was conducted using DistillerSR^© review software (Evidence Partners Incorporated, Ottawa, ON, Canada). Grey literature results were first screened independently using Microsoft Excel; those eligible after the first stage of full text review were transferred to DistillerSR^©.

Figure 1 shows a flowchart summarising the screening process. Two independent reviewers were involved in the screening process and the determination of eligibility criteria. The search process was not linear; rather the eligibility criteria were re-assessed after each round of screening based on the records remaining. After each round of screening the reviewers discussed how best to adapt the eligibility criteria for the next round. As mentioned, the initial search query and eligibility criteria were quite broad as we were unsure of the scope of existing literature. However, due to the large number of studies identified in the early stages of the review, eligibility criteria were narrowed throughout the process. The two reviewers independently assessed a sample of 10 abstracts on two occasions during the initial screening process and compared findings to ensure consistency in the application of the eligibility criteria. Table 2 outlines the final eligibility criteria. No limitations were placed on year of publication.

PRISMA flowchart.

Eligibility criteria.