A drug company is running trials on a new test for anabolic steroids. The company uses the test on 400 athletes know to be suing steroids and 200 athletes known not to be using steroids. Of those using steroids, the new test is positive for 390 and negative for 10. Of those not using steroids, the test is positive for 10 and negative for 190. What is the estimated probability of a false negative result (the probability that an athlete using steriodes will test negative)?

Question

A drug company is running trials on a new test for anabolic steroids. The company uses the test on 400 athletes know to be suing steroids and 200 athletes known not to be using steroids. Of those using steroids, the new test is positive for 390 and negative for 10. Of those not using steroids, the test is positive for 10 and negative for 190. What is the estimated probability of a  false negative  result (the probability that an athlete using steriodes will test negative)?

wach · Answer

So, we're finding the probability of essentially a wrong result. Out of each group, how many people were misdiagnosed out of the total number tested in that group?

anonymous · Answer

those using steroids only yielded 10 wrong results

anonymous · Answer

and also 10 tested positive when they were not using

anonymous · Answer

???

wach · Answer

Yes, and for the other group, 10 were also misdiagnosed. So we can say that there is a 20/800 chance of the results being wrong. But we only want to find the probability of a false negative. How can we make the probability of 20:800 more concise, only applying to negative results?

anonymous · Answer

by dividing the options for negative results?

wach · Answer

Yes: So if 20/800 represents the wrong result in both groups, we can isolate only the people with negative response (10 people). What is the probability?

anonymous · Answer

.00025

anonymous · Answer

?

wach · Answer

You want to find: 
(number of people who got false negative result) / (total number of people tested)

anonymous · Answer

.025 ok so 10/400

wach · Answer

It would be out of 800, because that is the total amount of people in the entire experiment.

anonymous · Answer

only 400 in the total exeriment tho

anonymous · Answer

?

anonymous · Answer

20/600?

anonymous · Answer

.975,.95,.05,.025 are my options

anonymous · Answer

10/600 gives me .016667

anonymous · Answer

??

wach · Answer

What is the estimated probability of a  false negative  result (the probability that an athlete using steriodes will test negative)?
Oh, so the probability is the misdiagnosed negative players / total athletes using steroids tested 
Thus, 0.025. 

I apologize for making this so confusing for you; the question confused me also.

anonymous · Answer

lol i know thats why i hatee probability ugh but everyone on here is so helpful !! whoever created this site is a genius.Thank you so much for clarifying for me your awesome!!

wach · Answer

You're welcome, and sorry for the confusion! >_<

anonymous · Answer

no problem thanks again i am going to become your fan if thats ok ?

anonymous · Answer

thanks again