TTEST Function

Basic Description

The Excel TTEST 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.

Syntax: TTEST( 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 must 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


Ttest Function Examples

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 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 Ttest function as follows :

=TTEST( 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 by :

=TTEST( A1:A12, B1:B12, 2, 1 )

This gives the result 0.898141379, which is double the probability associated with the one-tailed test.


Trouble Shooting

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

#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 the supplied type argument is not equal to 1, 2 or 3
#VALUE! Occurs if either the tails argument or the type argument is non-numeric

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