The Excel TINV Function

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Related Function:

TDIST Function

TINV & T.INV.2T

In Excel 2010, the TINV function has been replaced by the T.INV.2T function.

Although the Tinv function has been replaced, Excel 2010 has kept this function, (stored within the list of compatibility functions), for compatibility with earlier versions of Excel.

Basic Description

The Excel TINV 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 format of the function is :

TINV( 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 Student's T Distribution.
degrees_freedom	-	The number of degrees of freedom (must be ≥ 1)

Excel uses an iterative method to calculate the Tinv function and seeks to find a result, x, such that TDIST( x, degrees_freedom, 2 ) = probability.

Note that the Excel Tinv 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.

ie. The one-tailed inverse Student's T Distribution = TINV( 2*probability, degrees_freedom ).

Plot of Inverse of 2-Tailed Student's T Distribution with 10 Degrees of Freedom

2-Tailed Inverse Student's T-Distribution with 10 Degrees of Freedom

Examples

The chart on the right shows the 2-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 Tinv function, as follows:

=TINV( 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 :

=TINV( 0.5, 10 )

This gives the result 0.699812061.

Further information and examples of the Excel Tinv function can be found on the Microsoft Office website.