This may be particularly problematic for less experienced reviewers. Overall, our results suggest a lack of comprehensiveness of recommendations. The most frequent recommendations on data extraction are that extraction should be conducted by at least two people (17/25) that independent parallel extraction should be used (11/25) and that procedures to resolve disagreements between data extractors should be in place (14/25).

The most frequent recommendations on piloting extractions forms are that forms should be piloted on a sample of studies (18/25) and that data extractors should be trained in the use of the forms (7/25).

Across these sources the most common recommendations on form development are to use customized or adapted standardised extraction forms (14/25) provide detailed instructions on their use (10/25) ensure clear and consistent coding and response options (9/25) plan in advance which data are needed (9/25) obtain additional data if required (8/25) and link multiple reports of the same study (8/25). Our analysis includes recommendations from 25 documents: 4 SRO handbooks, 11 textbooks, 5 HTA method documents and 5 journal articles. One author extracted the recommendations and a second author checked them for accuracy. HTA documents were retrieved in February 2019 and database searches conducted in December 2019. We reviewed four types of sources: 1) methodological handbooks of systematic review organisations (SRO) 2) textbooks on conducting systematic reviews 3) method documents from health technology assessment (HTA) agencies and 4) journal articles. We reviewed guidance on the development and pilot testing of data extraction forms and the data extraction process.

Several studies have shown that data extraction errors are frequent in systematic reviews, especially regarding outcome data. This makes their development, pilot testing and use a crucial part of the systematic reviews process. Data extraction forms link systematic reviews with primary research and provide the foundation for appraising, analysing, summarising and interpreting a body of evidence.

Developmental screening form