Page 175 - Statistics II for Dummies

Chapter 9: Testing Lots of Means? Come On Over to ANOVA!
same graph. On the Same Scales for Graphs option, check the box for x and 159
the box for y. This option gives you the same scale on both the x and y axes
for all the histograms. Then click OK.

Histogram of Age Group 1, Age Group 2, Age Group 3, Age Group 4
36 39 42 45 48 51
Age Group 1 Age Group 2
20
15

10
5
Percent 20 Age Group 3 Age Group 4 0

15
10
5
0
Figure 9-2: 36 39 42 45 48 51
Checking
ANOVA
conditions Descriptive Statistics: Age Group 1, Age Group 2, Age Group 3, Age Group 4
by using
Total
histograms Variable Count Mean Variance
and Age Group 1 200 40.116 4.256
descriptive Age Group 2 200 41.880 4.994
Age Group 3 200 44.165 3.249
statistics. Age Group 4 200 47.405 5.154

Taking note of spread

The third condition for ANOVA is that the variance in each of the k popula-
tions is the same; statisticians call this the equal variance condition. You have
two ways to check this condition on your data:

✓ Calculate each of the variances from each sample and see how they
compare.
✓ Create one graph showing all the boxplots of each sample sitting side by
side. This type of graph is called a side-by-side boxplot. (See your Stats I
text or my book Statistics For Dummies (Wiley) for more information on
boxplots.)

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