Evidence-appraisal glossary
Adaptive trial design
An adaptive trial design is a clinical trial that lets researchers change specified features (like sample size, treatment arms, or randomization odds) partway through, based on planned interim looks at the accumulating data. Every possible change is defined in advance, so the trial stays statistically valid.
Also called: adaptive design, adaptive clinical trial, flexible trial design.
What it is
A fixed trial locks its design at the start and does not change until the end. An adaptive design builds in prospectively planned decision points where interim data can trigger prespecified changes: re-estimating sample size, dropping a losing arm, shifting randomization toward a promising arm, or stopping early for efficacy or futility.
How to read a study using it
- Was the plan prespecified? Legitimate adaptations are written into the protocol and statistical analysis plan before unblinding. Changes invented after seeing the data are not adaptive design; they are post hoc tinkering.
- Was the false-positive rate protected? Repeatedly looking at data inflates the chance of a spurious "significant" result. Look for stated methods (group-sequential boundaries, alpha-spending) that control overall type I error.
- Was interim access controlled? An independent data monitoring committee should hold interim results to keep the trial blinded.
- Watch stop-early effects. Trials halted early for benefit can overstate the effect size.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.