+ Reply to Thread
Results 1 to 5 of 5

Thread: no clue how to do this question

  1. #1
    Points: 735, Level: 14
    Level completed: 35%, Points required for next Level: 65

    Location
    Toronto
    Posts
    31
    Thanks
    0
    Thanked 0 Times in 0 Posts

    no clue how to do this question




    "The probability that any given person has a certain gene is 0.8 percent. Among people who have this gene, 80% test positively for it. Among people who do not have this gene, 5 percent test positively for it. What is the probability that a person who tested positively for the gene actually has the gene?"

    How do I go about solving this? Or rather how would I go about setting up the appropriate equations?

  2. #2
    Devorador de queso
    Points: 95,540, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Posting AwardCommunity AwardDiscussion EnderFrequent Poster
    Dason's Avatar
    Location
    Tampa, FL
    Posts
    12,930
    Thanks
    307
    Thanked 2,629 Times in 2,245 Posts

    Re: no clue how to do this question

    Have you learned about Bayes' theorem?
    I don't have emotions and sometimes that makes me very sad.

  3. #3
    Points: 735, Level: 14
    Level completed: 35%, Points required for next Level: 65

    Location
    Toronto
    Posts
    31
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: no clue how to do this question

    I have heard of it and I tried to use it here but I'm not doing it right.

    the probability of having the gene is P(G) = 0.008,

    the probability of having a positive test given that you have the gene P(Pos|G)= 0.8

    the probability having a false positive P(Pos|Gbar) where Gbar means you dont have the gene = 0.05

    and I want to find the probability of having the gene if you tested positive for it P(G|Pos)

    I can deconstruct any P(B|A) as P(B intersect A)/P(A) but in the case of testing positive for a gene what does P(Pos intersect G) mean? P(Pos|G) means 'probability of testing positive given that you have the gene" but P(Pos intersect G) means 'probability of testing positive AND having the gene' ...are these two the same in this case?
    Last edited by kingsolomonsgrave; 09-23-2013 at 03:11 PM.

  4. #4
    Devorador de queso
    Points: 95,540, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Posting AwardCommunity AwardDiscussion EnderFrequent Poster
    Dason's Avatar
    Location
    Tampa, FL
    Posts
    12,930
    Thanks
    307
    Thanked 2,629 Times in 2,245 Posts

    Re: no clue how to do this question

    In general we can write: P(A \cap B) = P(A|B)P(B)
    I don't have emotions and sometimes that makes me very sad.

  5. #5
    Points: 735, Level: 14
    Level completed: 35%, Points required for next Level: 65

    Location
    Toronto
    Posts
    31
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: no clue how to do this question


    i found Bay's theorem online and used that to answer the question. Thanks!

    http://en.wikipedia.org/wiki/Bayes'_theorem

+ Reply to Thread

           




Posting Permissions

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






Advertise on Talk Stats