Returns the probability associated with a Student's tTest. Use TTEST to determine whether two samples are likely to have come from the same two underlying populations that have the same mean.
Syntax
TTEST(array1,array2,tails,type)
Array1 is the first data set.
Array2 is the second data set.
Tails specifies the number of distribution tails. If tails = 1, TTEST uses the onetailed distribution. If tails = 2, TTEST uses the twotailed distribution.
Type is the kind of tTest to perform.
If type equals 
This test is performed 
1 
Paired 
2 
Twosample equal variance (homoscedastic) 
3 
Twosample unequal variance (heteroscedastic) 
Remarks
 If array1 and array2 have a different number of data points, and type = 1 (paired), TTEST returns the #N/A error value.
 The tails and type arguments are truncated to integers.
 If tails or type is nonnumeric, TTEST returns the #VALUE! error value.
 If tails is any value other than 1 or 2, TTEST returns the #NUM! error value.
 TTEST uses the data in array1 and array2 to compute a nonnegative tstatistic. If tails=1, TTEST returns the probability of a higher value of the tstatistic under the assumption that array1 and array2 are samples from populations with the same mean. The value returned by TTEST when tails=2 is double that returned when tails=1 and corresponds to the probability of a higher absolute value of the tstatistic under the “same population means” assumption.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example
 Create a blank workbook or worksheet.
 Select the example in the Help topic.
Note Do not select the row or column headers.
Selecting an example from Help
 Press CTRL+C.
 In the worksheet, select cell A1, and press CTRL+V.
 To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.

A 
B 
Data 1 
Data 2 
3 
6 
4 
19 
5 
3 
8 
2 
9 
14 
1 
4 
2 
5 
4 
17 
5 
1 
Formula 
Description (Result) 
=TTEST(A2:A10,B2:B10,2,1) 
Probability associated with a Student's paired tTest, with a twotailed distribution (0.196016) 
