Linking of search methods of origin for eligible studies

In addition to database searching, Hayden et al. used multiple supplementary search methods: a reference search of previously published systematic reviews, which were retrieved using a broader electronic search that did not include the prognostic factor concept; a forward search of publications citing identified prognostic factor measures; and hand searching, reference searching of included studies, and consultation of personal files to identify additional studies. To determine which studies would have been missed had any of the search strategy components been left out, we linked each included study in Hayden et al. to its search methods of origin, focusing only on those studies indexed in Ovid MEDLINE (n=58 of 60 total included studies).

To confirm which studies were retrieved by the focused electronic search strategy, we created a search string comprising the PubMed identifiers (PMIDs) of each of the fifty-eight included MEDLINE-indexed studies and combined it with the search that the team used. We consulted the team's search records to determine which studies had been retrieved by supplementary search methods. Finally, in addition to tracing the origin of each included study back to the search methods used in the review, we explored a hypothetical scenario in which only the broad electronic search strategy was used.