The Excel TTEST Function

Related Function:

TDIST function


TTEST and T.TEST

In Excel 2010, the TTEST function has been renamed T.TEST.

Although the Ttest 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 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.

The format of the function is :

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

  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 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.


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


Trouble Shooting

If you get an error from the Excel TTEST 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 tails argument or the type argument is non-numeric
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