Systematic Reviews: Data Extraction

Information about data extraction from reports

• Name of data extractors
• Date of data extraction
• Identification features of each report from which data are being extracted (first author, year)

Study methods

• Study design (parallel, factorial, crossover, cluster aspects of design for randomized trials, and/or study design features for non-randomized studies)
• Single or multicentre study; if multicentre, number of recruiting centres
• Recruitment and sampling procedures used (including at the level of individual participants and clusters/sites if relevant)
• Enrollment start and end dates; length of participant follow-up
• Statistical analysis 
  • Unit of analysis (individual participant, clinic, village, body part)
  • Statistical methods used
• Funding source(s), authors' financial relationship, or other COI

Participants

• Setting
• Regions(s) and country/countries from which study participants were recruited
• Study eligibility criteria, including diagnostic criteria
• Characteristics of participants at the beginning (or baseline) of the study (e.g. age, sex, comorbidity, socio-economic status)

Intervention

• Components, routes of delivery, doses, timing, frequency, intervention protocols, length of intervention
• Factors relevant to implementation (e.g. staff qualifications, equipment requirements)
• Integrity of interventions (i.e. the degree to which specified procedures or components of the intervention were implemented as planned)
• Description of co-interventions
• Definition of ‘control’ groups (e.g. no intervention, placebo, minimally active comparator, or components of usual care)
• For observational studies: description of how intervention status was assessed; length of exposure, cumulative exposure

Outcomes

• Measurement tool or instrument (including definition of clinical outcomes or endpoints); for a scale, name of the scale (e.g. the Hamilton Anxiety Rating Scale), upper and lower limits, and whether a high or low score is favourable, definitions of any thresholds if appropriate
• Specific metric (e.g. post-intervention anxiety, or change in anxiety from baseline to a post-intervention time point, or post-intervention presence of anxiety (yes/no))
• Method of aggregation (e.g. mean and standard deviation of anxiety scores in each group, or proportion of people with anxiety)
• Timing of outcome measurements (e.g. assessments at end of eight-week intervention period, events occurring during the eight-week intervention period)
• Adverse outcomes need special attention depending on whether they are collected systematically or non-systematically (e.g. by voluntary report)

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 (e.g. 2×2 table for dichotomous data; means and standard deviations for continuous data)
• Between-group estimates that quantify the effect of the intervention on the outcome, and their precision (e.g. risk ratio, odds ratio, mean difference)
• If subgroup analysis is planned, the same information would need to be extracted for each participant subgroup

Miscellaneous

• Key conclusions of the study authors
• Reference to other relevant studies
• Correspondence required
• Miscellaneous comments from the study authors or by the review authors