Implements a 2×2 Fishers exact test. Use this to test the independence of two categorical variables when the sample sizes are small.
For an approachable explanation of Fisher's exact test, see Fisher's exact test of independence by John H. McDonald in the Handbook of Biological Statistics.
The test is computed using code ported from Øyvind Langsrud's JavaScript implementation at http://www.langsrud.com/fisher.htm, used with permission.
use fishers_exact::fishers_exact;
let p = fishers_exact(&[1,9,11,3]).unwrap();
assert!((p.less_pvalue - 0.001346).abs() < 0.0001);
assert!((p.greater_pvalue - 0.9999663).abs() < 0.0001);
assert!((p.two_tail_pvalue - 0.0027594).abs() < 0.0001);