Identifying reports of randomized controlled trials (RCTs) in the Lancet: the contribution of the Cochrane Collaboration

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Clarke M, McDonald S, Lefebvre C

Introduction: Since 1993, the Cochrane Collaboration has contributed towards improving the retrieval of RCTs from MEDLINE in two important ways; by devising a highly sensitive search strategy, and by identifying reports of RCTs for retagging by the US National Library of Medicine (NLM). In 1994, following the reading of over 100,000 titles and abstracts from MEDLINE, 20,000 reports of RCTs were submitted to the NLM for inclusion in MEDLINE in 1995. MEDLINE is also being enhanced as a result of journal handsearching throughout the Collaboration. The Lancet was handsearched during 1995, and the retagged records were made available in MEDLINE in 1996.

Objective: A case study, using reports published in the Lancet in 1992, to identify the number of reports of RCTs correctly tagged by NLM, and the number of additional reports identified by the electronic search and the handsearch.

Methods: Reports of RCTs from the Lancet in 1992 were classified according to whether they had been tagged originally by NLM, retagged as a result of the search strategy, or retagged as a result of hand-searching.

Results: A search of MEDLINE in 1994 would have identified 100 Lancet records tagged as RCTs. An additional 7 records were retagged by 1995 as a result of the electronic search, and a further 18 were retagged by 1996 as a result of the handsearch. Of the 100 reports originally tagged as RCTs by NLM, 8 were not reports of RCTs, and therefore should not have been tagged as such.

Discussion: Even for a major journal such as the Lancet, 22% of RCTs may be missed by relying on NLM indexing alone. Further investigations will aim to identify whether there are systematic differences between the reports indexed as RCTs as a result of the three processes discussed above.