Systematic Reviews & Evidence Synthesis Methods

The process starts with your protocol, in which you:

1. Identify data categories to be used for coding and extraction.  It's the essential information you need to complete the review; for example, participant demographics, sample size, methods, interventions, and outcomes. 
2. Describe the methods you will use.

see RESOURCES (box to the right) to help you work through category identification and methods.

• Coding and extraction may be used during the second screening to help select eligible studies.
• Coding and extraction is required for evaluation of the final set of selected eligible studies.

Essential:

1. A Recording Form. Data categories are used to create a spreadsheet or special data collection form.
2. Consistency. information is recorded in a carefully determined format from each eligible study.  (Or, during screening, for every study still under consideration.)

• Coding refers to recording information such as who conducted the study and the design of the study.
• Extraction refers to recording the results of the study.

Recommended Practice:

• Pilot (test) your collection form to make sure it works as planned.
• Record data with synthesis in mind; that is, plan ahead for how you will be using the data.
• Record all information necessary to address the synthesis question, plus any additional information to help with critical appraisal.
  • Use a "notes" field to record important information that doesn't fit elsewhere.
  • Choose narrow categories over broad categories.  Think of age ranges; these can be combined later but will be hard to divide out later.
• But try to balance between under and over-extraction.
• Cochrane methodology advises having two people for most of this work and considers two a mandatory minium for recording results.
• Know that you may have to contact researchers for answers to questions not answered in reports of their research.

Examples of Forms for Coding & Extraction:

• See: Table 6.2 Data extraction table from Bernes et al (2015) --- look nearer the bottom of the page.
• Petticrew, M., & Roberts, H. (2008). Appendix 4: Example Data Extraction Form. In Systematic reviews in the social sciences: A practical guide. New York: Wiley. Retrieved from: https://onlinelibrary.wiley.com/doi/pdf/10.1002/9780470754887.app4
• Littell, J.H., Corcoran, J,. & Pillai, V. (2008). Appendix E: Screening and Data Extraction Form for Cochrane/Campbell Review of Effects of Multisystemic Therapy (MST). In Systematic Reviews and Meta-Analysis (pp. 160-172). New York: Oxford University Press.