Question

A dietary survey report indicates that the 5-year survival rate for breast cancer has increased following the introduction of a new screening method. However, autopsy data shows no change in overall mortality. What type of bias does this scenario illustrate?

• A. Survival bias
• B. Lead time bias
• C. Berksonian bias
• D. Detection bias

Hint:

Screening may increase measured survival time without reducing mortality. This is called lead time bias.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The scenario describes an illusion of benefit. The screening finds the disease earlier, so the patient "survives" for more years after diagnosis, but they still die at the same chronological time as they would have without screening.
Step 2: Detailed Explanation:

Definition of Lead Time: The interval between the detection of a disease by screening and the time when it would have been detected by clinical symptoms.

Mechanism of Lead Time Bias:

Suppose a person is destined to die at age 60.

Without screening: Diagnosed by symptoms at age 58. Survival = 2 years.

With new screening: Diagnosed at age 53. Survival = 7 years.


Even though the person died at the exact same age (60), the 5-year survival rate looks much better in the screened group. This is a statistical artifact.

Analyzing the scenario: The report says survival increased (due to early diagnosis) but mortality (death) didn't change. This perfectly illustrates lead time bias.

Contrast with other biases:

Length-time Bias: Occurs when screening catches slow-growing cases that would have had a better prognosis anyway.

Berksonian Bias: Selection bias where hospital-based patients are not representative of the community.


Step 3: Final Answer:
The increase in survival duration without a corresponding decrease in mortality, caused by earlier detection, is termed lead time bias.