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Abstract
Background: When conducting a systematic review, some data that need to be extracted from primary studies are presented only as figures. One can contact study authors to request original data from figures, but those requests for data seldom yield a response. In those circumstances data need to be extracted from figures. However, the Cochrane Handbook does not cover issues relating to data extraction from figures.
Objectives: To analyze whether protocols of Cochrane Systematic Reviews mention whether and how the authors will extract data from figures in included trials.
Methods: Cochrane Protocols published between May 2013 and May 2014 were screened by two authors independently and the following data were collected: date of protocol publication, country of authors’ origin, number of authors, number of affiliated institutions, Cochrane Review Group, whether the protocol contains description of data extraction from figures, the method of data extraction from figures, and literature references for a method of data extraction from figures.
Results: From a total of 589 protocols, 33 (5.6%) mentioned data extraction from figures in the Methods section. Most of those studies mentioning data extraction from figures (18/33) indicated that data from figures would be included only if two reviewers independently extracted the same result. Only one protocol specified that computer software would be used for data extraction from figures, and few stated estimation or approximation, while others did not provide any description of methodology for data extraction from figures. One protocol specifically indicated that data from figures would not be used, “because of [the] possibility of making measurement errors when estimating from graphs”.
Conclusion: Very few Cochrane Protocols mention data extraction from figures and, even when they do mention data that are presented only in figures, it is not necessarily to explain how those data will be extracted. Some even plan to disregard those data completely. The Cochrane Handbook and methodological standards for Cochrane Systematic Reviews should address methodology for extracting data from figures.
Objectives: To analyze whether protocols of Cochrane Systematic Reviews mention whether and how the authors will extract data from figures in included trials.
Methods: Cochrane Protocols published between May 2013 and May 2014 were screened by two authors independently and the following data were collected: date of protocol publication, country of authors’ origin, number of authors, number of affiliated institutions, Cochrane Review Group, whether the protocol contains description of data extraction from figures, the method of data extraction from figures, and literature references for a method of data extraction from figures.
Results: From a total of 589 protocols, 33 (5.6%) mentioned data extraction from figures in the Methods section. Most of those studies mentioning data extraction from figures (18/33) indicated that data from figures would be included only if two reviewers independently extracted the same result. Only one protocol specified that computer software would be used for data extraction from figures, and few stated estimation or approximation, while others did not provide any description of methodology for data extraction from figures. One protocol specifically indicated that data from figures would not be used, “because of [the] possibility of making measurement errors when estimating from graphs”.
Conclusion: Very few Cochrane Protocols mention data extraction from figures and, even when they do mention data that are presented only in figures, it is not necessarily to explain how those data will be extracted. Some even plan to disregard those data completely. The Cochrane Handbook and methodological standards for Cochrane Systematic Reviews should address methodology for extracting data from figures.