Obtaining t_alpha/2 Values

Most spreadsheets have a built-in function that returns the inverse of the Student's t distribution.

The function that returns the inverse of the Student's $t$ distribution is usually called TINV and takes two arguments:

• 1) The value of $\alpha$
• 2) The number of degrees of freedom $n$

The TINV function returns the value of $t_{\alpha/2}$ for a $t$ -distribution with $n$ degrees of freedom.

Important: Note that TINV always returns $t_{\alpha/2}$ , the threshold value for a two-tailed region.

The $t_{\alpha/2}$ value returned is interpreted as follows:

• The area under the bell curve of the $t$ -distribution from $-\infty$ to $-t_{\alpha/2}$ is $\alpha/2$ .
• The area under the bell curve of the $t$ -distribution from $t_{\alpha/2}$ to $\infty$ is $\alpha/2$ .