TTEST

TTEST(array1, array2, tails, type)

Returns the probability value from a t distribution.

array1	The first array.
array2	The second array.
tails	The number of distribution tails: 1 = one-tailed distribution 2 = two-tailed distribution
type	The kind of t-Test to perform: 1 = paired 2 = two sample equal variance (homoscedastic) 3 = two sample unequal variance (heteroscedastic)

REMARKS

* This function is only available for backwards compatibility and should not be used.
* T.TEST was added in Excel 2010 to replace this function.
* You can use this function to determine whether two samples are likely to have come from the same two underlying populations that have the same mean.
* If "array1" and "array2" have a different number of data points, and type = 1 (paired), then #N/A is returned.
* If "tails" is not an integer, it is truncated.
* If "tails" < 1, then #NUM! is returned.
* If "tails" > 1, then #NUM! is returned.
* If "tails" is not numeric, then #VALUE! is returned.
* If "type" is not an integer, it is truncated.
* if "type" < 1, then #NUM! is returned.
* If "type" > 3, then #NUM! is returned.
* If "type" is not numeric, then #VALUE! is returned.
* This is similar to the CHITEST, FTEST and ZTEST functions.
* For the Microsoft documentation refer to support.microsoft.com

	A
1	=TTEST({3, 4, 5, 8, 9, 1, 2, 4, 5}, {6, 19, 3, 2, 14, 4, 5, 17, 1}, 2, 1) = 0.196
2	=TTEST({1, 2, 3, 4, 5}, {1, 2, 3, 4, 5}, 2, 1) = #DIV/0!