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Table 5 Reasons why studies were missed by electronic search and handsearch

From: Which resources should be used to identify RCT/CCTs for systematic reviews: a systematic review

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]