Sponsored Links
Results 1 to 7 of 7
  1. #1
    hopeful786 is offline Member
    Join Date
    Feb 2005
    Posts
    120
    Downloads
    5
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Probability ques

    Advertisements



    a nw tst fr detect pros canc is neg in 95% of ptx who do not have the disease. If the tst is usde wth 8 consecutive bld sample taken from ptx without the dsesas, wht is the prob of getting at lest one post tst rslt?

    appologize for the misspels...

  2. #2
    rose.82 is offline Junior Member 510 points
    Join Date
    Sep 2006
    Posts
    67
    Downloads
    48
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Hi,

    I thinke the prob of getting at lest one positive test is:
    5%+5%+5%+5%+5%+5%+5%+5%=40%

  3. #3
    hopeful786 is offline Member
    Join Date
    Feb 2005
    Posts
    120
    Downloads
    5
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    close to the actual answer but not the right step
    I ll wait for others and then post...

  4. #4
    E2O
    E2O is offline Junior Member 510 points
    Join Date
    Feb 2007
    Posts
    40
    Downloads
    21
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    5 to the power 8
    sorry dont kn how to use the super script

  5. #5
    hopeful786 is offline Member
    Join Date
    Feb 2005
    Posts
    120
    Downloads
    5
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    The answer is

    1-(0.95^8)

    You have to multiply because the events are independent.

    I thought also to go the 0.5^8 route however it gives a very small probability when I actually calculated it, but I still don't know why this is wrong.

    Anyone can enlighten us?

  6. #6
    rose.82 is offline Junior Member 510 points
    Join Date
    Sep 2006
    Posts
    67
    Downloads
    48
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Hi,
    Oh, yes you are right 1-(.95^8)
    Because you want at least one test positive ,it means 1 positive or 2 positive or 3 positive,... .
    (.95^8) means all cases are negative and 1-(.95^8) means you calculate all situations except all negative.
    You can't use 0.5^8 because this means all tests positive not at least one positive.

  7. #7
    hopeful786 is offline Member
    Join Date
    Feb 2005
    Posts
    120
    Downloads
    5
    Uploads
    0
    Thanks
    0
    Thanked 0 Times in 0 Posts
    Okay now it makes sense, thnx.
    At least one test positive

    so
    0.95^8 = prob All test are negative.
    0.05^8 = prob All test are positive.
    1-(0.95^8) = prob of 1 or more positives.
    1-(0.05^8) = prob of 1 or more negatives.

Similar Threads

  1. First course in probability ebook
    By woowbagmaxode in forum Main Foreign Medical Schools Forum
    Replies: 0
    Last Post: 01-27-2011, 11:54 AM
  2. Physics Question + Admission Probability
    By mcvancouver in forum Saba University School of Medicine
    Replies: 4
    Last Post: 09-08-2008, 04:07 PM
  3. ques
    By PRS in forum USMLE Step 1 Forum
    Replies: 0
    Last Post: 11-18-2005, 02:20 PM
  4. more ques
    By Asclepius1 in forum USMLE Step 1 Exam Experiences
    Replies: 3
    Last Post: 03-18-2005, 08:52 PM
  5. ques
    By doppler in forum USMLE Step 1 Forum
    Replies: 1
    Last Post: 11-16-2004, 09:29 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •