Microsoft Office Tutorials and References

In Depth Information

**Testing to the T**

The arguments of the TTEST function are listed in Table 10-1.

Table 10-1

Arguments of the TTEST Function

Argument

Comment

Array 1

This is the reference to the range of the first array of data.

Array 2

This is the reference to the range of the second array of data.

Tails

Either a 1 or 2. For a one-tailed test, enter a 1. For a 2-tailed

test, enter a 2.

Type

Type of t-test to perform. The choice is a 1, 2, or 3. A number

1 indicates a paired test. A number 2 indicates a two-sample

test with equal variance. A number 3 indicates a two-sample

test with unequal variance.

The third argument of TTEST tells whether to conduct a one-tailed or

twotailed test. A one-tailed test is used when there is a question of whether one

set of data is specifically larger or smaller than the other. A two-tailed test is

used to tell whether the two sets are just different from each other without

specifying larger or smaller.

The first two arguments to TTEST are the ranges of the two sets of values. A

pertinent consideration here is how the two sets of data are related. The sets

could be comprised of elements that have a corresponding member in each

set. For example, there could be a set of “before” data and a set of “after” data.

Seedling

Height at Week 1

Height at Week 2

#1

4 inches

5 inches

#2

3
3
⁄
4
inches

5 inches

#3

4
1
⁄
2
inches

5
1
⁄
2
inches

#4

5 inches

5 inches

This type of data is entered into the function as
paired.
In other words, each

data value in the first sample is linked to a data value in the second sample.

In this case, the link is due to the fact that the data values are “before” and

“after” measurements from the same seedlings. Data can be paired in other

ways. In the salary survey, for example, each accountant may be paired with

a professor of the same age to ensure that length of time on the job does not

affect the results — in this case, you would also use a paired t-test.

When you’re using TTEST for paired samples, the two ranges entered for the

first and second arguments must be the same size. When you’re comparing

two independent (unpaired) samples, the two samples don’t have to be the

same size.