The Intention-to-Treat analysis (ITT analysis) is the standard methodological principle for the primary efficacy analysis in randomised controlled trials (RCTs). Under the ITT principle, all randomised participants are analysed in the group to which they were originally allocated – regardless of whether they actually received the treatment, adhered to the protocol, or discontinued the trial.
The ITT principle preserves the benefit of randomisation (comparability of the groups) and prevents a selection bias that would arise if only participants who fully completed the treatment were analysed. The Full Analysis Set (FAS) is, in practice, a pragmatic approximation of the strict ITT population and includes all randomised participants who received at least one dose and have at least one post-baseline measurement of the primary endpoint.
The ITT analysis is conservative and reflects effectiveness under real-world conditions. As a complementary sensitivity analysis, the Per-Protocol analysis (PP analysis) is often conducted, which includes only participants who complied with the protocol and estimates efficacy under ideal conditions. For CROs, the correct specification of analysis populations in the Statistical Analysis Plan (SAP) is a critical task. Regulatory reference: ICH E9, ICH E9(R1).