The day before study therapy intervention is defined as which study day according to CDISC ADaM models?

The correct answer is designated as Study day 0 because, according to the CDISC ADaM (Analysis Data Model) standards, Study day 0 is defined as the day on which the therapy intervention begins. This makes it a pivotal reference point for the treatment phase of a clinical trial. The day prior to this intervention, or the day before the therapy starts, is clearly marked as Study day -1.

In the context of clinical trials, the day of the first dose or intervention is crucial, and all other days are calculated in relation to this date. By accurately establishing which day corresponds to the intervention, researchers can uniformly track and report data that relates directly to the treatment phase, which is essential for clarity in data analysis and interpretation.

This convention ensures that there is a clear understanding of when treatment begins and allows for consistent data reporting across different studies. The other options do not align with the standard definitions, as Study day -1 refers to the day prior to intervention, which is not what the question asks for.