Table 5.

Reasons why studies were missed by electronic search and handsearch

Category	Reason	Studies citing reason (n = 42)
Electronic Resources
Indexing
	Inadequate indexing in general	16[3,27,29,32–44]
	Journal not indexed in resource	8[3,13,20,27,35,40,45,46]
	Not indexed with proper methodologic terms	9[21,26,28,29,32,36,42,47,48]
	Not indexed as RCT/CCT	7[35,37,49–53]
	Not indexed for any of the methodologic terms used by searchers	2[21,54]
	Database does not contain relevant index terms	2[17,50]
	Not indexed with any of the subheadings used in searches	1[21]
Search Strategy
	Insufficient or restricted search strategy	6[27,32,35,55–57]
Reporting
	Keywords or methodology not reported by author	9[13,19,29,34,41,48,53,58,59]
Database
	Issue(s) omitted from resource	4[3,26,56,60]
	Time lag in updating resource	2[60,61]
	Article(s) omitted or missing from resource	6[3,29,36,50,51,56]
Journal
	Published before database was created or beyond coverage years of database	2[56,60]
Other
	Unknown reason	6[26,38,38,54,60,62]
	Published as abstracts, books, book reviews, brief reports, letters, proceedings, supplements, etc.	9[20,26,38,38,49,51,56,63]
		• Wrong abstract assigned to reference[36] • Journals do not encourage authors to explicitly report methodology[37] • Length and complexity of search is limited using search engines[64] • Ongoing or recently finished studies[64] • Found through references[20] • Missed most Japanese reports[65] • Some personal communication did not get responses; organizations and people must be willing to supply trial information[18] • Not all abstracts are published in full[50] • Authors misspelled gingko[39] • Many RCTs are not identifiable in database[66]
Handsearch
	Handsearchers not trained properly	2[57,67]
	Methodologic terms "hidden" in article	1[26]
	Searcher fatigue, boredom	1[26]
	Journal not handsearched	2[35,42]
	Article not an RCT or CCT	1[54]
Other
	Different topic than what handsearchers were looking for	1[42]