Obtaining z_alpha/2 Values

Most spreadsheets have a built-in function that returns the inverse of the standard normal (or $z$ ) distribution.

The function that returns the inverse of the standard normal distribution is usually called NORMSINV and takes a single a argument: The value of $1-\alpha$

The formula =NORMSINV$(1-\alpha)$ returns the value of $z_{\alpha}$

The $z_{\alpha}$ value returned is interpreted as follows:

• The area under the bell curve of the $z$ -distribution from $z_\alpha$ to $\infty$ is equal to $\alpha$ .