Which of the following are characteristics of survival data?

• A. Strict left truncation, right skew distribution, and censored
• B. Only right censoring
• C. No censoring
• D. Only left truncation

Answer: (A)

Survival data revolve around time-to-event measurements where we don’t always know the exact event time for every subject. This leads to censoring, most often right censoring, because an event may not have occurred by the end of observation or the subject may be lost to follow-up. Many studies also involve delayed entry, where individuals enter the study at different times after the origin of time, creating left truncation. The observed survival times are typically right-skewed: many events happen relatively early, with a tail of longer survival times. So, the hallmark features are left truncation (delayed entry), a right-skewed distribution of survival times, and censoring together. The other options fail because they either ignore censoring, ignore truncation, or include only one aspect, missing the common combination seen in survival data.