Systematic Reviews & Meta-Analysis

Data extraction allows the systematic review team to see the data from each individual article to do a comparison of the studies. By collecting data from each study, you will be able to better describe the included studies, mitigate the risk of bias, and enable synthesis and meta-analysis.

A Data Collection Form will help gather the relevant details from each study. The form is usually developed in either Excel, Word, or using a separate tool. While each form may be tailored to your specific research question, the following details from each may be considered to be included:

• Study methods
  • Study design
  • Single or multicenter study
  • Recruitment and sampling procedures used
  • Enrollment start and end dates
  • Statistical analysis
• Participants
  • Setting
  • Region and country from which study participants were recruited
  • Study eligibility criteria
  • Characteristics of participants at the beginning or baseline of the study
• Intervention
  • Description of the intervention and comparison intervention
  • Factors relevant to implementation (e.g. staff qualifications, equipment requirements)
  • Description of co-interventions
  • Definition of ‘control’ groups (e.g. no intervention, placebo, etc.)
  • Components, dose, timing, frequency
  • For observational studies: description of how intervention status was assessed; length of exposure, cumulative exposure
• Outcomes
  • Whether there is evidence that the outcome was assessed
  • Measurement tool or instrument
  • Timing of outcome measurements
  • Adverse outcomes
• Results
  • For each group, and for each outcome at each time point: number of participants randomly assigned and included in the analysis; and number of participants who withdrew, were lost to follow-up or were excluded (with reasons for each)
  • Summary data for each group
  • If subgroup analysis is planned, the same information would need to be extracted for each participant subgroup

The following is an example of how you may construct your data extraction form. The example allows the ability to identify the PICO concepts of each study. The fields shown may be inputted into a table in Excel or Word, but keep in mind that they may need to be adapted for your specific research question:

The following are templates and tools that will help with data extraction:

Critical appraisal is the systematic analysis of research articles to determine the strength of the evidence in reference to your clinical question. Once you have screened and selected the final studies to be included in your systematic review, you may assess each for any risk of bias and how the studies were reported.

There are various critical appraisal tools that are specific to a given study design or research methodology. Below are select resources to locate critical appraisal tools and checklists

Li T, Higgins JPT, Deeks JJ (editors). Chapter 5: Collecting data. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.2 (updated February 2021). Cochrane, 2021. Available from www.training.cochrane.org/handbook.