Searching for observational studies: what does citation tracking add to PubMed? A case study in depression and coronary heart disease.
BACKGROUND
PubMed is the most widely used method for searches of the medical literature, but fails to identify many relevant articles. Electronic citation tracking offers an alternative search method.


METHODS
Articles investigating the role of depression in the aetiology and prognosis of coronary heart disease were sought through two methods: a) PubMed, and b) citation tracking where Science Citation Index was searched for all articles which cited ("forward citation tracking") or were cited by ("backward citation tracking") any of the articles in an index review. The number and quality of eligible articles identified by the two methods were compared.


RESULTS
50 articles that were not already included in the index review met our inclusion criteria; 11 were identified through Science Citation Index alone, 8 through PubMed alone, and 31 through both methods. Articles identified by Science Citation Index alone were published in higher impact factor journals, were larger and were less likely to show a positive association.


CONCLUSIONS
Science Citation Index identified more eligible articles than PubMed, and these differed qualitatively. Failing to use citation tracking in a systematic review of observational studies may result in bias.
International Centre for Eye Health, Clinical Research Unit, London School of Hygiene & Tropical Medicine, London, UK. hannah.kuper@lshtm.ac.uk
Hannah
H
Kuper
Amanda
A
Nicholson
Harry
H
Hemingway
D000043:Abstracting and Indexing; D015706:Bibliometrics; D003327:Coronary Disease / Q000209:etiology / Q000503:physiopathology* / Q000523:psychology / Q000628:therapy; D003866:Depressive Disorder / Q000150:complications*; D006801:Humans; D016247:Information Storage and Retrieval / Q000379:methods*; D019370:Observation; D017063:Outcome Assessment, Health Care; D010506:Periodicals as Topic; D011379:Prognosis; D011446:Prospective Studies; D039781:PubMed