Evidence guide
What Is a Control Group?
A control group estimates what would have happened without the tested intervention.
Controls take many forms
They may receive placebo, usual care, another treatment, a sham procedure or no intervention.
A poor comparison misleads
Comparing a new treatment with nothing can exaggerate benefit when attention, expectations or background care differ.
Controls in laboratory research
Positive controls show the system can detect an effect; negative controls reveal contamination, drift and nonspecific signals.
A practical reading checklist
- What exactly did the control receive?
- Were expectations and contact similar?
- Was usual care described?
- Were laboratory controls run alongside samples?