# Effective Population Size: Sex Ratio

The effective population size, N_{e}, is the size of a population that behaves like an
ideal (Wright-Fisher) population of size N_{e}. The sex ratio of a population affects
its effective population size. In a population with N_{m} males and N_{f}
females, the effective population size is:

$$N_e = {4 N_{m} N_{f} \over N}$$

The plot below shows how an unequal sex
ratio, expressed as the fraction of males in the population, reduces the
effective population size N_{e} (relative to the census population size N).

#### Code

```
var data=[];
var x_max = 1;
for (var i = 0; i <= x_max + 0.005; i = i + 0.01) {
var male_to_female_ratio = i;
Ne_to_N_ratio = 4 * male_to_female_ratio * (1 - male_to_female_ratio);
data.push(Ne_to_N_ratio);
}
draw_line_chart(data,"Proportion Males","Ne / N",[],x_max);
```

Note: the draw_line_chart function is built with D3.js
and can be found here.