An example

Table 2 exhibits data drawn from a study of phenotypic variation among individuals at the ABO blood locus:

Table 2: Data on variation in ABO blood type.

Phenotype	A	AB	B	O	Total
Observed	862	131	365	702	2060

The maximum-likelihood estimate of allele frequencies, assuming Hardy-Weinberg, is:²

$$\begin{eqnarray*} p_a &=& 0.281 \\ p_b &=& 0.129 \\ p_o &=& 0.590 \quad , \\ \end{eqnarray*}$$

giving expected numbers of 846, 150, 348, and 716 for the four phenotypes. $\chi^2_1 = 3.8$, $0.05 < p < 0.1$.