Can occur when medical technology advances and some cancers are diagnosed earlier in their progression than in the past.

• A. Lead time error
• B. Administrative data items
• C. Relevance of a data item
• D. Data dictionary

Answer: (A)

This is lead-time bias. When medical technology improves and cancers are found earlier, the clock starts earlier, so survival after diagnosis appears longer even if the patient doesn’t live any longer. For example, if a cancer would cause death at year 10, detecting it earlier at year 2 vs year 6 makes the time from diagnosis to death look longer (8 years vs 4 years) even though the actual death occurs at the same time. To assess true benefit, you’d look at mortality or cancer-specific death rates, not just longer survival after diagnosis.