## Sample size estimates for means in two independent samples

The formula to estimate the sample size required to estimate the mean of two independent samples is

```
$$
n_i =2\bigg(\frac{z\sigma}{E}\bigg)^2; i=1,2
$$
```

where

- $n_i$ is the sample size for $i^{th}$ group,
- $z$ is the $Z_{\alpha/2}$,
- $\sigma$ is the population standard deviation and
- $E$ is the margin of error.