Evidence-appraisal glossary
Group-Sequential Design
A trial design that plans a series of interim looks at the accumulating data, with pre-set rules that allow early stopping for benefit, harm, or futility while protecting the overall error rate.
Also called: group sequential trial, sequential design.
Rather than analyzing only once at the end, a group-sequential design schedules several analyses and defines statistical boundaries the data must cross to stop early. An alpha-spending function keeps the study-wide false-positive risk at the intended level despite the repeated testing. This lets trials end sooner when the evidence is decisive, sparing participants unnecessary exposure, but results that stop very early for benefit can overstate the true effect size. Readers should note how many looks were planned and which boundary triggered any early stop.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.