A test for a virus correctly identifies someone who has the virus (by returning a positive result) 99% of the time. The overall population is 1,000,000 people. The test correctly identifies someone who does not have the virus (by returning a negative result) 99% of the time. It is known that 0.5% of the population has the virus. A doctor decides to treat anyone who tests positive for the virus. Is this a good decision?

Question

anonymous · Answer

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jim_thompson5910 · Answer

`It is known that 0.5% of the population has the virus`

`The overall population is 1,000,000 people`

how many people have the virus?

anonymous · Answer

500,000?

jim_thompson5910 · Answer

0.5% = 0.005

multiply 0.005 by 1 million

anonymous · Answer

5000

jim_thompson5910 · Answer

yep so 995,000 don't have the virus

jim_thompson5910 · Answer

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jim_thompson5910 · Answer

`A test for a virus correctly identifies someone who has the virus (by returning a positive result) 99% of the time`

so if you have the virus, then there is a 99% chance that the test gets it right

that means 0.99*5000 = 4,950 people will get tested positive (the ones who have the virus)

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jim_thompson5910 · Answer

1% will test negative 

0.01*5000 = 50

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