Can data extraction from figures perform a meta-analysis?

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Abstract text
Background: Systematic reviews (SR) with the statistical methods of meta-analysis represent the highest level on the evidence to make decision. Extracting data can be a problem when randomized clinical trials (RCT) publish figures as the only source of outcome data. Thus, none included RCTs in the SRs can be lost to perform meta-analysis. In this way, alternative methods to data extraction need to be developed.

Objectives: To analyze the precision of alternative methods (rule and software) to data extraction from figures to perform meta-analysis.

Methods: All data were produced in a statistical package and were generated 14 RCTs. Figures were generated from same RCTs; mean and 95% confidence interval (CI) were used as statistical parameters from figures to elevated the complexity of data extraction; standard deviations was obtained applying the equation: “Sqrt(N) x (upper limit of CI - lower limit of CI) / 3.92”. Differences between researchers (VS and AJG) to data extraction were previously compared. Using other datas, one blind researcher (AJG) performed data extraction from figures with a simple rule (Figure 1a) and another blind researcher (VS) performed the data extraction with the Digitizelt software (Figure 1b). Meta-analyses were performed and compared with data extracted from a rule, software and original data.

Results: There are absence of differences (Chi² = 0.01, df. = 1, P = 0.93; I² = 0%) between researchers (VS and AJG) to data extraction. The meta-analyses results are presented through the Figure 2.

Conclusions: The alternative methods, such as rule and software, evaluated in this study to procedure data extraction from figures showed high precision and seem to be useful as a option to perform meta-analysis when RCTs publish figures as the only source of outcome data. The authors are planning further studies—using real data from a SR—to confirm these results.
Silva V1, Carvalho APVD1, Grande AJ1, Martimbianco ALC1, Riera R1, Atallah AN1
1 Brazilian Cochrane Centre, Brazil
Presenting author and contact person
Presenting author: 
Valter Silva
Contact person Affiliation Country
Valter Silva (Contact this person) Brazilian Cochrane Centre Brazil