Fisher's Exact Test

http://en.wikipedia.org/wiki/Fisher%27s_exact_test

The test is useful for categorical data that result from classifying objects in two different ways; it is used to examine the significance of the association (contingency) between the two kinds of classification. So in Fisher's original example, one criterion of classification could be whether milk or tea was put in the cup first; the other could be whether Ms Bristol thinks that the milk or tea was put in first. We want to know whether these two classifications are associated – that is, whether Ms Bristol really can tell whether milk or tea was poured in first. Most uses of the Fisher test involve, like this example, a 2 × 2 contingency table