Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

Libniz Group Title

Suppose that for the general population, 1 in 5000 people carries the human immunodeficiency virus (HIV). A test for the presence of HIV yields either a positive () or negative () response. Suppose the test gives the correct answer 99% of the time. What is P[-|H], the conditional probability that a person tests negative given that the person does have the HIV virus? What is P[H|+], the conditional probability that a randomly chosen person has the HIV virus given that the person tests positive?

  • 2 years ago
  • 2 years ago

  • This Question is Closed
  1. Libniz Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    @satellite73

    • 2 years ago
  2. Libniz Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    P[-|H]= P[- * H] / P[H] .01/(1/5000)

    • 2 years ago
  3. Libniz Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    is it right?

    • 2 years ago
  4. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    this is a baye's formula problem, right?

    • 2 years ago
  5. Libniz Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    yes

    • 2 years ago
  6. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    easiest way to see the answer is to do it with actual numbers. then we can use the formula, although i have to go soon.

    • 2 years ago
  7. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    suppose 1,000,000 people are tested. of those 1,000,000, exactly 200 will have the disease (assuming the probabilities are exact) then of those 200, 99% will test positive, that is, 198 will test positive, and 2 will test negative. out of the remaining 999,800 1% or 99,980 will also test positive

    • 2 years ago
  8. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    that was wrong, sorry. last line should be out of the remaining 999,800 1% or 9,998 will test positive

    • 2 years ago
  9. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    now you can just go ahead and compute

    • 2 years ago
  10. Libniz Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    so that 1% accuracy is shared among those wrongly tested positive and wrongly tested negative or it is each 1%?

    • 2 years ago
  11. Libniz Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    1% inaccuracy

    • 2 years ago
  12. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    that is what i am assuming from the wording, yes

    • 2 years ago
  13. Libniz Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    ok thanks

    • 2 years ago
  14. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    usually false positive and false negative are different percents, but in this case you were just given one number

    • 2 years ago
  15. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    9998+200 test positive, but of those with positive tests, only 198 actually have the disease, so the probability that you have the disease given that the test is positive is only \(\frac{198}{9998+200}\) now if you redo the problem using only decimals instead of 1,000,000 you will get bays formula

    • 2 years ago
    • Attachments:

See more questions >>>

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.