MyFisher24

A very compact routine to compute Fisher's exact test on a 2x4 matrix

Fisher's exact test of 2x4 contingency tables permits calculation of precise probabilities in situation where, as a consequence of small cell frequencies, the much more rapid normal approximation and chi-square calculations are liable to be inaccurate. The Fisher's exact test involves the computations of several factorials to obtain the probability of the observed and each of the more extreme tables. Factorials growth quickly, so it's necessary use logarithms of factorials. This computations is very easy in Matlab because x!=gamma(x+1) and log(x!)=gammaln(x+1). This function is now fully vectorized to speed up the computation. Actually, the function also computes the mid-P correction to make the test less conservative.