A blood test is 99% accurate in detecting a disease. However, 0.1% of the population actually has the disease. If a person tests positive, the approximate probability they actually have the disease is:
A blood test is 99% accurate in detecting a disease. However, 0.1% of the population actually has the disease. If a person tests positive, the approximate probability they actually have the disease is:
- A. 99%
- B. 90%
- C. 9%
- D. 1%
Answer: C) 9%
Explanation: P(Disease|Positive) = (0.001 × 0.99) / [(0.001 × 0.99) + (0.999 × 0.01)] = 0.00099 / 0.01098 ≈ 0.0901 or ~9%.
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