Microsoft Office Tutorials and References

In Depth Information

**Testing to the T**

Use TTEST to determine the probability that two samples come from the same

population.

Here’s how to use the TTEST function:

1. Enter two sets of data.

2. Position the cursor in the cell where you want the result to appear.

3. Enter
=TTEST(
to start the function.

4. Drag the pointer over the first list, or enter the address of its range.

5. Enter a comma (
,).

6. Drag the pointer over the second list, or enter the address of its range.

7. Enter a comma (
,).

8. Enter a
1 for a one-tailed test, or enter a
2 for a two-tailed test.

9. Enter a comma (
,).

10. Enter one of the following:

•1 for a for a paired test

•2foratestoftwosampleswithequalvariance

•3foratestoftwosampleswithunequalvariance

11. Enter a
).

If you ever took a statistics course, you may recall that a t-test returns a

t-value,
which you then had to look up in a table to determine the associated

probability. Excel’s TTEST function combines these two steps. It calculates

the t-value internally and determines the probability. You never see the actual

t-value, just the probability — which is what you’re interested in anyway!

The TDIST function returns the probability for a given t-value and degrees

of freedom. You would use this function if you had a calculated t-value and

wanted to determine the associated probability. Note that the TTEST

function doesn’t return a t-value but rather a probability, so you wouldn’t use

TDIST with the result that is returned by TTEST. Instead, you would use

TDIST if you had one or more t-values calculated elsewhere and needed to

determine the associated probabilities.

TDIST takes three arguments:

✓
The t-value

✓
The degrees of freedom

✓
The number of tails (1 or 2)