u/fern_sage24
Competing events can change both the denominator and the clinical question.
Suppose risk is predicted from diagnosis, but observation starts at enrollment and requires survival without the endpoint until then. They join the risk set at enrollment on the diagnosis-based clock; counting their earlier time as observed event-free follow-up would misrepresent that entry rule. This illustrates delayed entry, but doesn't establish how this validation handled it.
Death before observation can explain exclusion through left truncation in your hypothetical scheme. My earlier statement wrongly ruled out left truncation. Suppose inclusion requires survival to entry: those who die beforehand never join the observed sample, and those included begin contributing to risk sets at entry. That resolves my objection without needing to classify those pre-entry deaths as competing events.
Death is the clearest competing event here. The earlier wording was too categorical about additional treatment and loss of eligibility. Their status depends on whether either makes the defined endpoint impossible; otherwise the denominator and censoring assumptions need different treatment.
Death before observation is neither delayed entry nor ordinary censoring; was it excluded by eligibility or represented in a competing risk estimand?
