In a negative binomial experiment is almost the same as that of a binomial experiment, with only one difference: in a binomial experiment has a fixed number of tests.
If one of the following five conditions are met, the experiment is a binomial:
For a fixed number of n trials.
Each of the test shall be carried out independently of each other.
There are only two possible outcomes (Success or Failure).
The probability of success (p), for each of the tests has been resolved.
The Random variable Y= the number of successes along the way.
For example: in a standard deck of cards, shuffle them up, and then select a card. To replace the memory, and repeat it twenty times. Where Y is the number of tricks that can help you out.
The negative binomial distribution is similar to that of the binomial distribution using two-movements (especially of the numbers from 1 to 5 in the above list).
The total number of samples, n, is constant.
The Random variable Y= the number of trials needed to achieve the success of the year.