Data extraction is an important part of systematic reviews and meta-analyses. However, it may occur that published randomized controlled trials (RCTs) present numerical data only in figures (e.g. Kaplan-Meier survival curves).
While it is a good and common practice for authors of systematic reviews to contact and request the missing information from authors of studies, rarely this process result in obtaining the information needed.
The Cochrane Handbook does not provide guidance on how to extract data from figures. Studies demonstrated that extracting data from figures with software is faster and achieve higher interrater
reliability than manual extraction (1).
Plotdigitizer is an online data extraction tool that allows users to extract data from images in numerical format (https://plotdigitizer.com/app), but many others are available online.
It is recommended to use these tools only if contacting study authors fails to acquire original data. If these tools are used, it is recommended that two investigators perform data extraction independently.
References
- Jelicic Kadic A, Vucic K, Dosenovic S, Sapunar D, Puljak L. Extracting data from figures with software was faster, with higher interrater reliability than manual extraction. J Clin Epidemiol. 2016;74:119-123. doi:10.1016/j.jclinepi.2016.01.002
