Once the search and selection of studies for inclusion is completed the next step is to read the full text of each article identified for inclusion in the Systematic Review and extract the relevant data using a standardised data extraction form. The purpose of the data extraction step is to:
The standardised data extraction form is as long or as short as necessary and can be coded if desired, especially if a quantitative analysis is required. If the Systematic Review is a narrative (no meta-analysis) and/or reviews a relatively small number of studies, coding is probably unnecessary.
Ideally, at least two reviewers should work independently, to extract quantitative and other critical data from each study, and a fair procedure for resolving discrepancies should be established.
Tools available for data extraction include an Excel spreadsheet or the data extraction templates in software like Covidence. If the Systematic Review includes a meta-analysis and/or reviews a large number of studies the data extraction software will likely be helpful. Using the excel spreadsheet allows for more customisation of what data to collect.
Reviewers should develop the standardised form to suit the specific Systematic Review1 and use the key question(s) and inclusion and exclusion criteria as a guide. Use the PICOT framework to choose data elements in the data extraction form. Anticipate what the data summary table will need to include.
The following is an example of elements to include in a standardised data extraction form.
|
Citation |
Include details such as journal, title, author, volume, page numbers etc. |
|
Objective |
Describe the study objective as stated by the authors |
|
Population |
Demographic detail of the participants in the study |
|
Intervention |
Describe the intervention or treatment |
|
Comparison |
Describe the control group or comparison intervention |
|
Outcome |
Record the results of the intervention and how measured |
|
Type |
Study Type / Design - eg. Randomised Control Trial |
|
Comments |
Notes in regard to the study quality for grading |
Completed data extraction forms can be used to produce a summary table of study characteristics that were considered important for inclusion in the Systematic Review.
The completed summary table should be included in the Results section of the Report of the Systematic Review, either as an appendix or the in the body of the text.
1. Institute of Medicine of the National Acadamies. (2011). Finding what works in health care: Standards for systematic reviews. Available: http://iom.nationalacademies.org/Reports/2011/Finding-What-Works-in-Health-Care-Standards-for-Systematic-Reviews/Standards.aspx
2. Hathorn, E., et al. (2014). The effectiveness of gentamicin in the treatment of Neisseria gonorrhoeae: A systematic review. Systematic Reviews, 3, 1, 104. Available: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4188483/