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Negative Binomial

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  • Negative Binomial

    Can anyone please confirm if these formulas are correct for negative binomial, thanks.

    pdf = [ (x+r-1) nCr (x) ](p^r) (q^x)
    cdf = ∑ pdf
    E(x) = r*q/p
    var(x) = r*q/(p^2)
    mgf = [p/(1-q*e^t)]^(x+1)

  • #2
    A good place to check wikipedia or mathworld.wolfram.com

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    • #3
      I checked and they give me 2 different answer.
      Thats why I want to verify if this is correct, thanks

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      • #4
        Well wikipedia disagrees with you right?

        Now in the mathworld link, it might look different but write out (x+r-1) C (r-1) and compare that to (x+r-1) C (x). You should be able to prove they are the same.

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