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University Library, University of Illinois at Urbana-Champaign

Evidence-Based Medicine (EBM)

SYNTHESES, SYNOPSES, SUMMARIES (Secondary or Pre-appraised Evidence)

Systematic Review

Identifies, appraises and synthesizes all [quality] empirical evidence that meets pre-specified eligibility

•Define an appropriate question/problem
•Search the literature
•Published & unpublished
•Collect the data
•Synthesize collective data
•Placing the findings in context


•Statistical technique for combining findings from independent studies
•Combined results produce an overall statistic
•“Precise estimate” of treatment effect, taking into consideration the size of the different studies
•Validity of the meta-analysis depends on the quality of the studies that are included

Practice Guidelines

Clinical practice guidelines are systematically developed statements to assist practitioner and patient decisions about appropriate health care for specific clinical circumstances.” (Institute of Medicine, 1990)

Systems -patient-specific, evidence-based, computerized decision support

Evidence Summaries  - summaries of evidence for decision making; includes comprehensive information for common clinical topics


Randomised Controlled Trial - clinical study in which subjects are randomly assigned to groups; one group is the experimental intervention and other(s) is the control (alternative or placebo). Provides indication of effectiveness.

  • Comparison Study
  • Random allocation (reduces bias)
  • Used for effect of an intervention (statistical analysis)
  • Expensive; reliant on volunteers; ethically considerations


Cohort Study - observational study that follows a group and looks at differences in outcome of interest within the group. Retrospective studies look at suspected risk factor (causation). Prospective studies track risk factor or outcome of interest; very difficult to control for all variables

  • Groups have been either exposed or not to some factor of interest
  • Use for risk factors for disease
  • Easy
  • May be hidden confounders

Case Control - observational study that matches a group based on a common condition or exposure and compares them to a group without the condition or exposure; may show correlation but not necessarily causation.

  • One group with specific condition is compared to group without
  • Fast & cheap
  • Relies on recall and self-report

Cross-sectional Study - descriptive study the measures prevalence or determinants of health in a specific population in a given time frame; used to explore or propose explanation for health-related issue

Case Series - a set of cases from clinicians that are all related to a specific disease or issue; may lead to subsequent clinical trials

Case Reports - one report related to a specific health issue of an individual patient


Overview of the design tree

Figure 1 shows the tree of possible designs, branching into subgroups of study designs by whether the studies are descriptive or analytic and by whether the analytic studies are experimental or observational. The list is not completely exhaustive but covers most basics designs.