Editing Negative binomial distribution (section)

===Cumulative distribution function===

The [[cumulative distribution function]] can be expressed in terms of the [[regularized incomplete beta function]]:<ref name="Wolfram" /><ref name="Cook" />
: <math>
    F(k; r, p) \equiv \Pr(X\le k) = I_{p}(r, k+1).
  </math>
(This formula is using the same parameterization as in the article's table, with {{mvar|r}} the number of successes, and <math>p=r/(r+\mu)</math> with <math>\mu</math> the mean.)

It can also be expressed in terms of the [[cumulative distribution function]] of the [[binomial distribution]]:<ref>Morris K W (1963),A note on direct and inverse sampling, Biometrika, 50, 544–545.</ref>
: <math>
    F(k; r, p) = F_\text{binomial}(k;n=k+r,1-p).
  </math>