Article type
Year
Abstract
Objective: To describe a typical Cochrane review in terms of the number of studies listed as included studies, ongoing studies and studies awaiting assessment. To use this information to provide an estimate of how many Cochrane reviews would be needed to assess all studies currently listed in The Cochrane Controlled Trials Register (CENTRAL).
Methods: 989 reviews from The Cochrane Database of Systematic Reviews in The Cochrane Library, Issue 1, 2001 were analysed for the number of included studies, ongoing studies and studies awaiting assessment per review. Included studies are those meeting eligibility criteria for the review, and where information is included. The number of references cited per study was extracted from a random sample of reviews.
Results: The 989 Cochrane reviews contained 9,778 included studies, with the typical Cochrane review containing 6 studies (based on the median number per review). 17% of reviews listed ongoing studies that met review criteria but where the results of the study were not yet available for inclusion. 29% of reviews listed studies awaiting assessment of whether these should be included in the review. The number of references per study within Cochrane reviews was used to provide an estimate of the number of trials referenced by 300,00 reports in CENTRAL. This was used to provide an estimate of the number of additional Cochrane reviews that would be needed for systematic reviews to cover all these studies.
Conclusions: 9,778 trials were included in 989 Cochrane reviews in The Cochrane Library, Issue 1, 2001. A typical Cochrane review included 6 studies and 6.6 references. With an average Cochrane review containing six studies, this would correspond to 45,000 Cochrane reviews being needed to cover the more than 300,000 references in CENTRAL (approximately 270,000 studies). It is, however, possible that 1.1 references per study is an underestimate. For example, the Cochrane Stroke Group found an average of 2.1 in their Specialized Register of Stroke Trials (4,525 reports corresponding to 2,132 studies). On the basis of this figure, the number of additional Cochrane reviews would be estimated as 24,000. In addition not all references in CENTRAL or the studies they report, might be suitable for new Cochrane reviews. There will be references to studies already within Cochrane reviews and some references appear more than once. In addition some of the studies will relate to interventions that are no longer used or information that is not relevant to health care decisions, and some studies may be eligible, but not yet included, in existing Cochrane reviews. Given that 45,000 may be a gross overestimate, it is difficult to know how many Cochrane reviews would be needed, but we predict that at least another 10,000 Cochrane reviews are needed to cover a substantial proportion of the studies relevant to health care that have already been identified
Methods: 989 reviews from The Cochrane Database of Systematic Reviews in The Cochrane Library, Issue 1, 2001 were analysed for the number of included studies, ongoing studies and studies awaiting assessment per review. Included studies are those meeting eligibility criteria for the review, and where information is included. The number of references cited per study was extracted from a random sample of reviews.
Results: The 989 Cochrane reviews contained 9,778 included studies, with the typical Cochrane review containing 6 studies (based on the median number per review). 17% of reviews listed ongoing studies that met review criteria but where the results of the study were not yet available for inclusion. 29% of reviews listed studies awaiting assessment of whether these should be included in the review. The number of references per study within Cochrane reviews was used to provide an estimate of the number of trials referenced by 300,00 reports in CENTRAL. This was used to provide an estimate of the number of additional Cochrane reviews that would be needed for systematic reviews to cover all these studies.
Conclusions: 9,778 trials were included in 989 Cochrane reviews in The Cochrane Library, Issue 1, 2001. A typical Cochrane review included 6 studies and 6.6 references. With an average Cochrane review containing six studies, this would correspond to 45,000 Cochrane reviews being needed to cover the more than 300,000 references in CENTRAL (approximately 270,000 studies). It is, however, possible that 1.1 references per study is an underestimate. For example, the Cochrane Stroke Group found an average of 2.1 in their Specialized Register of Stroke Trials (4,525 reports corresponding to 2,132 studies). On the basis of this figure, the number of additional Cochrane reviews would be estimated as 24,000. In addition not all references in CENTRAL or the studies they report, might be suitable for new Cochrane reviews. There will be references to studies already within Cochrane reviews and some references appear more than once. In addition some of the studies will relate to interventions that are no longer used or information that is not relevant to health care decisions, and some studies may be eligible, but not yet included, in existing Cochrane reviews. Given that 45,000 may be a gross overestimate, it is difficult to know how many Cochrane reviews would be needed, but we predict that at least another 10,000 Cochrane reviews are needed to cover a substantial proportion of the studies relevant to health care that have already been identified