Fooled by Randomness

[Tangled up in Blue]

If a test for some disease is 95% accurate,and the disease affects one person in a thousand,and you go for a test and it comes back positive,what's the probability that you have the disease?

Answers and your reasoning please.

 

[Hotman]

If a test for some disease is 95% accurate,and the disease affects one person in a thousand,and you go for a test and it comes back positive,what's the probability that you have the disease?

Answers and your reasoning please.

about 2% - reason, I'm right because I always am x

 

[Berrichonne shrimper]

Whats this got to do with travel cards?

 

[Pubey]

If a test for some disease is 95% accurate,and the disease affects one person in a thousand,and you go for a test and it comes back positive,what's the probability that you have the disease?

Answers and your reasoning please.

A test can't be 95% accurate, a diagnostic test is defined by sensitivity and specificity.

Sensitivity = The probability of getting a TRUE POSITIVE. i.e. the probability of the test saying positive when the person has the disease

Specificity = The probability of getting a TRUE NEGATIVE. i.e. the probability of the test saying negative when the person doesn't have the disease.

A 100% accurate test (i.e. 100% sensitivity and specificity) will mean that there are never any false positive or false negative results.

I assume that in your question you can't have false negatives, but I'll let someone else solve it because this is what I do for a day job.

 

[MK Shrimper]

Is the answer 42 or is that something else? :unsure:

 

[Rob Noxious]

0/10.

Reason: to be cheerful.

 

[Tangled up in Blue]

about 2% - reason, I'm right because I always am x

Correct but I don't agree with your reasoning. :raspberry:
"The correct answer is 2 per cent,because if you test 1,00 people,the test will give fifty positives,whereas only one of the population actually has the illness."
John Lanchester.Whoops!(Thanks to Yogi for the heads up on this excellent book).:thumbsup:
(eg drawn from Taleb's Fooled by Randomness).

 

[Tangled up in Blue]

0/10.

Reason: to be cheerful.

Surely Reasonsto be cheerful.:winking:

 

[Tangled up in Blue]

Is the answer 42 or is that something else? :unsure:

The meaning of life/universe etc:winking:

 

[Tangled up in Blue]

Whats this got to do with travel cards?

Try thinking outside the box sometimes,Tony.:winking:

 

[Stuart W]

If a test for some disease is 95% accurate,and the disease affects one person in a thousand,and you go for a test and it comes back positive,what's the probability that you have the disease?

Answers and your reasoning please.

If your test is positive, and the test is 95% accurate, then there is a 95% chance that you have the disease. The fact that it affects one in a thousand, one in a hundred, even one in two, is irrelevant. Obviously to derive the accuracy rate of 95%, all people that tested positive were then monitored to see how many actually had the disease, and it came to 95%. You are bringing in a further factor which has nothing to do with the probability.
I thank you.

 

[davewebbsbrain]

Is the answer 42 or is that something else? :unsure:

About half of the best band ever

 

[Pubey]

If your test is positive, and the test is 95% accurate, then there is a 95% chance that you have the disease. The fact that it affects one in a thousand, one in a hundred, even one in two, is irrelevant. Obviously to derive the accuracy rate of 95%, all people that tested positive were then monitored to see how many actually had the disease, and it came to 95%. You are bringing in a further factor which has nothing to do with the probability.
I thank you.

well at least one person fell into the trap!

 

[Tangled up in Blue]

well at least one person fell into the trap!

Most people do.That's the point.Including Doctors when Taleb originally posed this question.

 

[Mad Cyril]

Better to be fooled by randomness than fooled by a bogus gas board official.

 

[BLUEBLOOD]

Better to be fooled by randomness than fooled by a bogus gas board official.

Or an Encyclopedia Salesman

 

[Davros]

 

[Neil_F]

I'm glad you are reading Taleb, Barna. Hopefully it will demonstrate to you why socialism and planned economies are intellectually bankrupt.

 

[Tangled up in Blue]

I'm glad you are reading Taleb, Barna. Hopefully it will demonstrate to you why socialism and planned economies are intellectually bankrupt.

Neil,
You missed the point.He's quoted in John Lanchester's "Whoops!:Why everyone owes everyone and no one can pay".I suspect JL is (secretly) one of my lot.

 

[Neil_F]

I didn't read the whole thread. My mistake.

I do recommend you read Taleb though.