The Negative Binomial distribution describes the distribution of the number of failures in order to achieve a specified number of successes, with a specified probability of success for each attempt. As such, by definition, it is dimensionless. It is frequently used in actuarial models.
The distribution requires two inputs, the Number of Successes (which must be a dimensionless positive integer) and the Probability of Success. Like the Poisson distribution, the Negative Binomial is a discrete distribution consisting of only integer values.
Note: Since this is a discrete distribution, the PDF view does not
actually display a probability density
function. Instead, it displays a probability
mass function.