The **Negative Binomial Distribution** is used for modeling rates of occurrence.
The Negative Binomial distribution has two parameters:

- r = the total number of failures.
- = P("success").

**Example:**
A process that manufactures widgets is monitored.
As each widget exits the process line, it is tested for defective versus non-defective.
On the fifth defect, the process is stopped for re-adjustment.
The random variable *X* follows a Negative Binomial distribution with *r* = 5 and = P(widget is non-defective).