Evidence-appraisal glossary
Intention-to-treat
Intention-to-treat analyzes trial participants in the group they were randomized to, regardless of whether they finished, switched, or followed the treatment. By preserving the original random groups, it keeps randomization's protection against bias and estimates the effect of assigning the treatment, which reflects how it tends to perform when prescribed rather than under perfect adherence.
Also called: ITT, intent-to-treat, intention to treat.
Intention-to-treat (ITT) is an analysis rule: everyone who was randomized is counted in their originally assigned group, even if they stopped the treatment, took the other arm's treatment, or never started. Keeping people in their assigned groups preserves the balance created by randomization, because dropouts and non-adherers are often different from those who comply, and removing them can bias the result. ITT estimates the effect of assigning the treatment, which reflects real conditions where people miss doses and change course. When reading a trial, check whether the primary analysis was truly ITT and how missing outcome data were handled, since large losses to follow-up can still distort even an ITT analysis. Compare it with any per-protocol analysis the authors report. Example: in a trial where many drug-arm patients quit because of side effects, ITT keeps those quitters in the drug group, giving an honest estimate of what prescribing the drug achieves. Ask whether all randomized participants were accounted for.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.