# The Excel T.TEST Function

Related Function:
T.DIST Function

## Function Description

The Excel T.Test function calculates the probability associated with the Student's T Test, which is commonly used for identifying whether two data sets are likely to have come from the same two underlying populations with the same mean.

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

The syntax of the T.Test function is:

T.TEST( array1, array2, tails, type )

where the function arguments are:

array1 - The first data set.
array2 - The second data set (must have the same length as array1).
tails -

The number of tails for the distribution. This can be either:

 1 - Uses the one-tailed distribution 2 - Uses the two-tailed distribution
type -

An integer that represents the type of t-test. This can be either:

 1 - Paired T-Test 2 - Two-sample equal variance T-Test 3 - Two-sample unequal variance T-Test

## T.Test Function Examples

A B
1 4 8
2 5 3
3 2 7
4 5 3
5 8 5
6 9 2
7 3 2
8 2 7
9 3 9
10 8 4
11 9 4
12 5 7

Columns A and B of the above spreadsheet on the right contain two arrays of data.

The probability associated with the Student's paired t-test with a one-tailed distribution, for the two arrays of data can be calculated using the Excel T.Test function as follows:

=T.TEST( A1:A12, B1:B12, 1, 1 )

This gives the result 0.449070689.

The probability associated with the Student's paired t-test with a two-tailed distribution, for the same two arrays of data, is calculated as follows:

=T.TEST( A1:A12, B1:B12, 2, 1 )

This gives the result 0.898141379.

Note that the probability associated with the two-tailed T-Test is double that of the one-tailed T-Test.

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

## T.Test Function Errors

If you get an error from the Excel T.Test Function, this is likely to be one of the following:

Common Errors
 #N/A - Occurs if the two supplied arrays have different lengths. #NUM! - Occurs if either: The supplied tails argument has any value other than 1 or 2 or The supplied type argument is not equal to 1, 2 or 3. #VALUE! - Occurs if either the supplied tails argument or the supplied type argument is non-numeric.