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Homework Help: Help with NETICA needed

  1. Apr 1, 2010 #1
    Assume that a narcotics test gives positive results in 99% for drug users. For people not
    using narcotics the test gives negative results in 98% of cases. A company decided to test its employees knowing that 0.5% of them use drugs. Estimate the probability that a person with a positive test result is indeed a user. Estimate using the NETICA software.

    Hi, I'm studying Civil Engineering and now I have some humanity courses. For subject Decision Making and Negotiation Theory I have to do above problem. Can anyone know Netica and can help me? Thx.
  2. jcsd
  3. Apr 1, 2010 #2


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    Dang! I don't even know what NETICA stands for, let alone know how to use it. Of course, I suppose you aren't allowed to just use Bayes rule...so easy...

    Welcome to physics forums.
  4. Apr 3, 2010 #3
    Well, the first task was to use Bayes formula and I did this like that:

    P(U) = 0.5%
    P(N) = 99.5%
    P(CU|U) = 99.0%
    P(CN|U) = 1.0%
    P(CU|N) = 2.0%
    P(CN|N) = 98.0%

    P(U|CU) = [P(CU|U)*P(U)] / P(CU)
    P(U|CU) = [P(CU|U)*P(U)] / [P(CU|U)*P(U) + P(CU|N)*P(N)]
    P(U|CU) = [99% * 0.5%] / [99% * 0.5% +2.0% * 99.5%]
    P(U|CU) = 19.92%

    Is that correct?

    Due to norsys.com website 'Netica, the world's most widely used Bayesian network development software, was designed to be simple, reliable, and high performing.' While for me isn't because I don't know how to use it.
  5. Apr 3, 2010 #4


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    Yes, your calculation is correct, although I would have expressed the algebra with decimals instead of percents. Remember, probabilities are numbers in the interval [0,1].
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