What is Fishers Exact Test and when should I use it?
Fisher’s Exact test is a procedure that you can use for data in a two by two contingency table. It is an alternative to the Chi-square test. A two by two contingency table arises in a variety of contexts, most often when a new therapy is compared to a standard therapy (or a control group) and the outcome measure is binary (live/dead, diseased/healthy, infected/uninfected, etc.). (My added note… “new is compared to a standard…” … a comparison or difference. OMU) Fisher’s Exact Test is based on exact probabilities from a specific distribution (the hypergeometric distribution). The Chi-square test relies on a large sample approximation. Therefore, you may prefer to use Fishers Exact test in situations where a large sample approximation is inappropriate.
Fisher’s Exact test is a procedure that you can use for data in a two by two contingency table. It is an alternative to the Chi-square test. A two by two contingency table arises in a variety of contexts, most often when a new therapy is compared to a standard therapy (or a control group) and the outcome measure is binary (live/dead, diseased/healthy, infected/uninfected, etc.). Fisher’s Exact Test is based on exact probabilities from a specific distribution (the hypergeometric distribution). The Chi-square test relies on a large sample approximation. Therefore, you may prefer to use Fishers Exact test in situations where a large sample approximation is inappropriate. There’s really no lower bound on the amount of data that is needed for Fisher’s Exact Test. You do have to have at least one data value in each row and one data value in each column. If an entire row or column is zero, then you don’t really have a 2 by 2 table. But you can use Fisher’s Exact Test when one of the cells in
