Contents

Abstract
Background
Methods
Results
- Study selection
- Study characteristics
- Results of individual studies
- Studies that did not implement a data extraction system
- Studies that identified sentences but did not extract data elements from abstracts only
- Studies that identified only sentences but did not extract data elements from full-text reports
- Studies that identified data elements only from abstracts but not from full texts
- Studies that identified data elements from full-text reports
- Risk of bias across studies
Discussion
Conclusions
Appendix 1
Competing interests
Authors’ contributions
Funding/Support
Role of the sponsors
Disclaimer
Additional contributions
Author details
References