Article type
Year
Abstract
Background: To minimize bias due to the selective availability of data, systematic reviews need to identify as many relevant studies as possible to provide reliable evidence. Although many reports of trials are included in major bibliographic databases, such as MEDLINE and EMBASE, identifying them has proved problematic. In 1996, a search strategy was derived by Carol Lefebvre and Steve McDonald [1] from an analysis of how frequently terms were used in EMBASE records to describe reports of randomized trials, that had been identified by handsearching the BMJ and the Lancet for 1990 and 1994.
Objectives: To identify reports of randomized trials in EMBASE using a search strategy of terms, tested for sensitivity and precision; and to contribute these to the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library.
Methods: Search terms, from the 1996 analysis, with a precision of over 40%, together with terms with a sensitivity of over 10% for 1990 and over 15% for 1994, were selected. They included the following free-text terms: random$, crossover$, cross-over$, cross over$, factorial$, placebo$, doubl$ adj blind$, singl$ adj blind$, allocat$, assign$, volunteer$; and the following index terms: crossover procedure, double-blind procedure, randomized controlled trial, single-blind procedure. These terms were used to identify reports of randomized trials in EMBASE using online database providers offering access to MEDLINE and EMBASE simultaneously so that records which were already coded as reports of trials in MEDLINE (and were, therefore, already included in CENTRAL) could be excluded. Records were downloaded for the period 1974-2002. The titles and abstracts were read to identify reports of randomized trials and checked by a second experienced handsearcher before inclusion in CENTRAL.
Results: During 1997 and 1998, 30,000 reports of trials were identified [2]. Since then, a further 30,000 have been identified. In total, approximately 240,000 records have been downloaded from EMBASE and records for all 60,000 reports of randomized trials are included in CENTRAL.
Conclusions: The analysis used to derive the original search strategy was based on a small dataset and the terms were derived subjectively. The final part of this project involves an objective analysis of the frequency of terms used to describe the reports of trials that have been identified, compared with their frequency across the entire EMBASE database, to estimate their sensitivity and precision in identifying reports of randomized trials. This analysis will be used to generate a highly sensitive search strategy for EMBASE with which to complete the project. It will be available for use within The Cochrane Collaboration and elsewhere.
References: 1. Lefebvre C, McDonald S. Development of a sensitive search strategy for reports of randomized controlled trials in EMBASE. Fourth International Cochrane Colloquium; 1996 Oct 20-24; Adelaide, Australia. p. A28. 2. Paul N, Lefebvre C. Reports of controlled trials from EMBASE: an important contribution to The Cochrane Controlled Trials Register. Sixth International Cochrane Colloquium; 1998 Oct 22-26; Baltimore, Maryland, USA. p. 85.
Objectives: To identify reports of randomized trials in EMBASE using a search strategy of terms, tested for sensitivity and precision; and to contribute these to the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library.
Methods: Search terms, from the 1996 analysis, with a precision of over 40%, together with terms with a sensitivity of over 10% for 1990 and over 15% for 1994, were selected. They included the following free-text terms: random$, crossover$, cross-over$, cross over$, factorial$, placebo$, doubl$ adj blind$, singl$ adj blind$, allocat$, assign$, volunteer$; and the following index terms: crossover procedure, double-blind procedure, randomized controlled trial, single-blind procedure. These terms were used to identify reports of randomized trials in EMBASE using online database providers offering access to MEDLINE and EMBASE simultaneously so that records which were already coded as reports of trials in MEDLINE (and were, therefore, already included in CENTRAL) could be excluded. Records were downloaded for the period 1974-2002. The titles and abstracts were read to identify reports of randomized trials and checked by a second experienced handsearcher before inclusion in CENTRAL.
Results: During 1997 and 1998, 30,000 reports of trials were identified [2]. Since then, a further 30,000 have been identified. In total, approximately 240,000 records have been downloaded from EMBASE and records for all 60,000 reports of randomized trials are included in CENTRAL.
Conclusions: The analysis used to derive the original search strategy was based on a small dataset and the terms were derived subjectively. The final part of this project involves an objective analysis of the frequency of terms used to describe the reports of trials that have been identified, compared with their frequency across the entire EMBASE database, to estimate their sensitivity and precision in identifying reports of randomized trials. This analysis will be used to generate a highly sensitive search strategy for EMBASE with which to complete the project. It will be available for use within The Cochrane Collaboration and elsewhere.
References: 1. Lefebvre C, McDonald S. Development of a sensitive search strategy for reports of randomized controlled trials in EMBASE. Fourth International Cochrane Colloquium; 1996 Oct 20-24; Adelaide, Australia. p. A28. 2. Paul N, Lefebvre C. Reports of controlled trials from EMBASE: an important contribution to The Cochrane Controlled Trials Register. Sixth International Cochrane Colloquium; 1998 Oct 22-26; Baltimore, Maryland, USA. p. 85.