Opportunities and challenges in using studies without a control group in comparative effectiveness reviews

Area of Science:

• Health Services Research
• Clinical Epidemiology

Background:

• Comparative effectiveness research (CER) aims to identify optimal therapeutic interventions.
• Single group studies, lacking concurrent comparison groups, are often excluded from CER.

Purpose of the Study:

• To explore the utility of single group studies in CER.
• To outline assumptions for interpreting single group studies in CER.

Main Methods:

• Review of methodologies for using single group studies in CER.
• Discussion of extrapolation techniques and validity assessments.

Main Results:

• Single group studies can provide causal effect information through extrapolation.
• Validity hinges on careful case-by-case examination of implicit or historical comparisons.

Conclusions:

• Circumstances exist where single group studies are acceptable evidence for CER.
• Systematic reviewers must understand the challenges and assumptions in interpreting these designs.