Fisher's exact test

$p_{i.} = \frac{n_{i.}}{n}$

$p_{ij} = p_{i.}p_{j.}$

$O_{ij} = $ Number of observed sample in $(,j)$

$\chi^2 = \sum_i\sum_j\frac{(O_{ij} - E_{ij})^2}{E_{ij}}$

Clustering