Information Technology Reference
In-Depth Information
2.
How many samples are you comparing? If you are comparing two sam-
ples, use a t test. If you are comparing three or more samples, use an
analysis of variance (also called ANOVA).
2.4.1 Independent Samples
Perhaps the simplest way to compare means from independent samples is using
confidence intervals, as shown in the previous section. In comparing the confi-
dence intervals for two means, you can draw the following conclusions:
Iftheconfidenceintervals don't overlap , you can safely assume the two
means are significantly different from each other (at the confidence level
you chose).
Iftheconfidenceintervals overlap slightly , the two means might still be
significantly different. Run a t test to determine if they are different.
Iftheconfidenceintervals overlap widely , the two means are not signifi-
cantly different.
Let's consider the data in Figure 2.3 to illustrate running a t test for inde-
pendent samples. This shows the ratings of ease of use on a 1 to 5 scale for
two different designs as rated by two different groups of participants (who were
assigned randomly to one group or the other). We've calculated the means and
confidenceintervalsandgraphedthose.Butnotethatthetwoconfidenceinter-
vals overlap slightly: Design 1's interval goes up to 3.8, whereas Design 2's goes
down to 3.5. This is a case where you should run a t test to determine if the two
means are significantly different.
Figure 2.3 Example of a t test on independent samples.
Search WWH ::




Custom Search