Intention-to-treat (ITT) and per-protocol analysis
Analysing every patient in the group they were randomised to, whether or not they actually took the treatment. It preserves the fairness of randomisation and reflects what happens when a treatment is prescribed in real life; per-protocol analysis, by contrast, counts only those who complied.
ITT is the primary analysis for superiority trials because excluding non-compliers or early dropouts reintroduces bias. Per-protocol analyses matter for non-inferiority trials, where non-compliance can mask a real difference. 'Modified ITT' variants exclude patients who never received a dose or lacked a baseline measurement and should be pre-specified. 'Response-evaluable' populations in single-arm trials inflate response rates by dropping early progressors, and 'safety population' counts patients as treated. Trial and drug pages on this site report ITT results unless stated.