Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    A certain medical condition affects one in a thousand of the population. A screening procedure is developed that is 95% accurate. Discuss the probability that you have the condidtion if the screening procedure says that you do.
    Offline

    14
    This seems a little easy for an interview question? There is simply a 2% chance you have the condition.
    Offline

    2
    ReputationRep:
    (Original post by Kolya)
    This seems a little easy for an interview question? There is simply a 2% chance you have the condition.
    I think it's intended to be a "trick question" in that some candidates may just say 95%. And the fact that the results of a test with 95% accuracy only gives you a 2% chance of actually having the medical condition is quite surprising, too.
    Offline

    1
    ReputationRep:
    I'm not very clever, and not applying to oxbridge.

    Will someone just explain as to how its a 2% chance.

    Ta. =]
    Offline

    14
    Take 1000 people. 1 will be expected to have the condition. (999x5 + 1x95)/100 will be expected to be diagnosed, which is very close to 1000x5/100 = 50 - close enough, given the significant figures of the data. Hence 1 people will have the condition, 50 will be diagnosed, so there is a 1/50 = 2% chance of having the condition if you are diagnosed as having it.
    Offline

    14
    Reminds me of a demonstration yesterday in the series of maths lectures at UCL...
    Offline

    0
    ReputationRep:
    In fact given this values the more accurate solution is 1.87% , but the algoritm is pretty much the same.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: November 29, 2012

1,559

students online now

800,000+

Exam discussions

Find your exam discussion here

Poll
Should predicted grades be removed from the uni application process
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.