Censoring Survival Data

In survival data, censoring leads to incomplete data, and it typically occurs when subjects experience an event before or after the study ends.

Right-censoring is the most typical form, and it occurs when the subject drops out of the study before the event occurs or when the study ends before the event occurs.

For example, a clinical study on the occurrence of heart attacks is carried out for five years. If the subjects do not have a heart attack, the data is right-censored.

Left-censoring is relatively rare but can occur when the beginning of an event is unknown or when the event happens before the subjects participate in the study.

For instance, in a study of cancer recurrence following treatment, if subjects are examined five months post-treatment for recurrence, those who have a recurrence are left-censored.

Interval censoring occurs when a specific subject is studied for a period, gets lost to follow-up for a while, and returns to continue being studied.