sample proportion
# with attribute
$$\hat{p}=\frac{1}{n}\sum^{n}{i=1}X{i}$$
$n=\text{sample size}$
$\sum^{n}{i=1}X{i}=\text{sum of indicator variables}$
$X_{i=}\begin{cases}1\text{ : if sample member }i\text{ has the attribute}\0\text{ : otherwise}\end{cases}$