Data extraction is a crucial part of a systematic review. It enables the assessment of the validity of the included items and assists with the appraisal, analysis, and interpretation required to complete the review.
You need to have a clear idea of which data elements are necessary for your analysis and how to manage and store your data. The Cochrane Handbook outlines the types of data that should be collected for health and medical systematic reviews.
Additionally you should consider what tools you will use to analyse the data you have. If you use a systematic review tool such as Covidence, it can provide a framework and assist you with the data extraction process.
The approach you take for your data depends on whether you are working with included items that use similar methodologies or with items that use different methodologies.
Similar Methodologies: If the items are similar, you can combine the outcomes through statistical methods in a meta-analysis.
Different Methodologies or Qualitative Research: if the items have different methodologies or you are dealing with qualitative research, you will need to undertake a meta-synthesis to combine results.