title: Effectiveness of different databases in identifying studies for systematic reviews: experience from the WHO systematic review of maternal morbidity and mortality.
abstract: BACKGROUND
  Failure to be comprehensive can distort the results of a systematic review. Conversely, extensive searches may yield unmanageable number of citations of which only few may be relevant. Knowledge of usefulness of each source of information may help to tailor search strategies in systematic reviews.
  
  
  METHODS
  We conducted a systematic review of prevalence/incidence of maternal mortality and morbidities from 1997 to 2002. The search strategy included electronic databases, hand searching, screening of reference lists, congress abstract books, contacting experts active in the field and web sites from less developed countries. We evaluated the effectiveness of each source of data and discuss limitations and implications for future research on this topic.
  
  
  RESULTS
  Electronic databases identified 64098 different citations of which 2093 were included. Additionally 487 citations were included from other sources. MEDLINE had the highest yield identifying about 62% of the included citations. BIOSIS was the most precise with 13.2% of screened citations included. Considering electronic citations alone (2093), almost 20% were identified uniquely by MEDLINE (400), 7.4% uniquely by EMBASE (154), and 5.6% uniquely by LILACS (117). About 60% of the electronic citations included were identified by two or more databases.
  
  
  CONCLUSIONS
  This analysis confirms the need for extending the search to other sources beyond well-known electronic databases in systematic reviews of maternal mortality and morbidity prevalence/incidence. These include regional databases such as LILACS and other topic specific sources such as hand searching of relevant journals not indexed in electronic databases. Guidelines for search strategies for prevalence/incidence studies need to be developed.
authors.affiliation: UNDP/UNFPA/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Department of Reproductive Health and Research, World Health Organization, Geneva, (1211) Switzerland. betrana@who.int
authors.forename: Ana P
authors.initials: AP
authors.lastname: Betrán
authors.forename: Lale
authors.initials: L
authors.lastname: Say
authors.forename: A Metin
authors.initials: AM
authors.lastname: Gülmezoglu
authors.forename: Tomas
authors.initials: T
authors.lastname: Allen
authors.forename: Lynn
authors.initials: L
authors.lastname: Hampson
mesh_terms: D005260:Female; D006801:Humans; D016206:Databases, Bibliographic / Q000145:classification / Q000592:standards; D015994:Incidence; D016247:Information Storage and Retrieval; D008428:Maternal Mortality; D008429:Maternal Welfare; D016239:MEDLINE; D010506:Periodicals as Topic / Q000592:standards; D015995:Prevalence; D012107:Research Design; D014944:World Health Organization; D000078202:Systematic Reviews as Topic