The Excel T.TEST Function

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Basic 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 a renamed version of the TTEST function, that is available in earlier versions of Excel.

The format 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

Examples

Columns A and B of the 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.

Further information and examples of the Excel T.Test function are provided on the Microsoft Office website.