A diagnostic test has been introduced that will detect a ceain disease 1 year earlier than it is usually detected. Which of the following is most likely to happen to the disease within 10 years after the test is introduced? (Assumed that early detection has no effect on the natural history of the disease. Also assume that no changes in death ceification practises occur during the 10 years.)

**Core Concept**
The question is testing the understanding of lead time bias, a type of bias that occurs in cohort studies when a screening test detects a disease at an earlier stage than it would have been detected without screening. This can artificially inflate the apparent effectiveness of the screening test.

**Why the Correct Answer is Right**
Lead time bias occurs when the screening test detects the disease earlier than it would have been detected without screening, but the disease still follows its natural course. In this scenario, the disease will still occur within the same time frame, but it will be diagnosed 1 year earlier. However, the disease will still be reported as occurring within the same time frame, as the death certification practices have not changed. This means that the incidence of the disease will appear to increase in the short term, but this is an artifact of the lead time bias.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because lead time bias does not affect the overall incidence of the disease in the long term. The disease will still occur within the same time frame, but it will be diagnosed earlier.

**Option B:** This option is incorrect because lead time bias does not affect the mortality rate of the disease. The disease will still have the same mortality rate, but it will be diagnosed earlier.

**Option C:** This option is incorrect because lead time bias does not affect the natural history of the disease. The disease will still follow its natural course, but it will be diagnosed earlier.

**Option D:** This option is incorrect because lead time bias does not affect the overall mortality rate of the disease. The disease will still have the same mortality rate, but it will be diagnosed earlier.

**Clinical Pearl / High-Yield Fact**
Lead time bias can be a problem in cohort studies when evaluating the effectiveness of screening tests. It's essential to consider this bias when interpreting the results of such studies.

**Correct Answer: A.**

✓ Correct Answer: B. The apparent 5-year survival rate will increase