Search and selection process. Two search phases will be conducted to provide evidence to contribute jointly to the narrative synthesis. The database search and the gray literature search will be performed concurrently, with the results of both being selected based on the screening checklist. Gray literature will be rejected at the screening stage if it is not considered to be of sufficient relative importance (categories 1 and 2 in Table 1) as determined by AcademyHealth . Gray literature reports describing empirical research will be placed in the narrative synthesis if deemed to have sufficient quality (Category A as per McGrath et al. .