Searching for observational studies: what does citation tracking add to PubMed? A case study in depression and coronary heart disease

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.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.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.Highly sensitive methods have been developed for the identification of randomised trials, but there are few guidelines for searching for observational studies. [1] Many research questions can only be addressed through observational studies, for instance the deleterious effects of psychiatric diseases or smoking, and so a review of such a topic would rely on searching for observational studies. PubMed is the most widely used database for searches and is freely available. PubMed may miss many relevant articles and this could influence the conclusions drawn. [2,3] Science Citation Index offers a potential complement to PubMed, particularly in the common situation when at least one review has already been carried out. Once such an index review on the topic in question is identified, Science Citation Index can be used to identify all the articles that cited ("forward citation tracking") or were cited by ("backward citation tracking") the articles in the index review. No p