What does censoring mean in survival analysis?

• A. The event has occurred for all participants.
• B. Censoring occurs only when a participant withdraws consent.
• C. Censoring occurs when the event has not occurred by study end or loss to follow-up.
• D. Censoring means the data were missing at random and imputed.

Answer: (C)

In survival analysis, censoring happens when we don’t know the exact time of the event for some participants because the study ends or they drop out before the event occurs. We only know that they were event-free up to the time they left or up to the end of follow-up. This partial information is still useful and is incorporated into survival estimates without assigning a definite event time to those individuals. The other ideas don’t fit: one would mean the event happened for everyone, which isn’t censoring; censoring isn’t limited to withdrawal, and imputing missing data is a separate approach rather than what censoring means in this context. Censoring is typically right-censoring—the most common form—where the event has not occurred by the last observed time.