# The Excel T.INV.2T Function

## Function Description

The Excel T.INV.2T function calculates the inverse of the two-tailed Student's T Distribution, which is a continuous probability distribution that is frequently used for testing hypotheses on small sample data sets.

The T.INV.2T function is new to Excel 2010. However, this function is simply an updated version of the TINV function, which is available in earlier versions of Excel.

The syntax of the T.INV.2T function is:

T.INV.2T( probability, degrees_freedom )

Where the function arguments are:

 probability - The probability (between 0 and 1) for which you want to evaluate the inverse of the two-tailed Student's T Distribution. degrees_freedom - The number of degrees of freedom (must be ≥ 1).

Note that:

• Excel uses an iterative method to calculate the result of the T.Inv.2t function, and seeks to find a result, x, such that T.DIST.2T( x, degrees_freedom ) = probability.
• The Excel T.Inv.2t Function calculates the inverse of the two-tailed Student's T Distribution. If you want to calculate the inverse of the one-tailed t-distribution you can simply double the probability.

I.e. The one-tailed inverse Student's T Distribution = T.INV.2T( 2*probability, degrees_freedom ).

## T.Inv.2t Function Examples 2-Tailed Inverse Student's T-Distribution with 10 Degrees of Freedom

The above chart on the right shows the two-tailed Inverse Student's T Distribution with 10 degrees of freedom.

If you want to calculate the value of this function for a probability of 0.25, this can be done using the Excel T.Inv.2t function, as follows:

=T.INV.2T( 0.25, 10 )

This gives the result 1.221255395.

If you want to calculate the value of the one-tailed inverse Student's T-Distribution for a probability of 0.25, this can be done by doubling the probability, as follows:

=T.INV.2T( 0.5, 10 )

which gives the result 0.699812061.

For further information and examples of the Excel T.Inv.2t function, see the Microsoft Office website.

## T.Inv.2t Function Errors

If you get an error from the Excel T.Inv.2t function this is likely to be one of the following:

Common Errors
 #NUM! - Occurs if either:The supplied probability is ≤ 0 or > 1  orThe supplied degrees_freedom is < 1. #VALUE! - Occurs if one or both of the supplied arguments are non-numeric.