It is estimated that 0.3% of a large population have a particular disease.

hi i cant work this out

Its is estimated that 0.3% of a large population have a particular disease. a test developed to detected the disease gives a false positive in 4% of tests and a false negative in 1% of tests. a person is tested positive for the disease. what is the probability that the person actually has the disease?

markosheehan said:

hi i cant work this out

Its is estimated that 0.3% of a large population have a particular disease. a test developed to detected the disease gives a false positive in 4% of tests and a false negative in 1% of tests. a person is tested positive for the disease. what is the probability that the person actually has the disease?

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markosheehan said:

hi i cant work this out

Its is estimated that 0.3% of a large population have a particular disease. a test developed to detected the disease gives a false positive in 4% of tests and a false negative in 1% of tests. a person is tested positive for the disease. what is the probability that the person actually has the disease?

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I'm not sure exactly what you are asking. If it really is "what is the probability that the person actually has the disease?", isn't that the 0.3%? Is what you are asking really "what is the probability that a person tested negative actually has the disease?"


Assuming the latter, sometimes, to work a sadistics* problem, you can just start out with say, a 1000 [or 10000, or ...] sample experiment which follows the values exactly. Thus
\(\displaystyle \text{Total population Tested = 1000 }
\begin{cases}
False Positive& 40\\
False Negative& 10\\
True Negative& 9030\\
True Positive& 20
\end{cases}
\)
So, total number tested negative is? Number tested negative who actually have the disease?

BTW: Do you know what False Positive, False Negative, etc. mean?

*Yes! Sadistics

maths probability question

hi i cant work this out

Its is estimated that 0.3% of a large population have a particular disease. a test developed to detected the disease gives a false positive in 4% of tests and a false negative in 1% of tests. a person is tested positive for the disease. what is the probability that the person actually has the disease?

i was told my teacher that the answer is (probability of having the disease)/(probability the test is positive)
i can work out the probability of having the disease(.003) but i cant work out the probability of the test being positive