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Chapter 16: One-Way Analysis of Variance
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Table 16-2:
Relief Time for Headache
for the three groups of Patients
Before we use the ANOVA procedure to determine whether the average
relieve time for the three different drugs are the same, the validity of the
ANOVA assumptions should be checked. This must be done so that the
inference made on the population means will be reliable.
Solution:
Graphical displays will be used to help check the validity of the
ANOVA assumptions of normality and the constant variance.
Figure 16-8
displays a histogram for the three data sets.
By analyzing
Figure 16-8
, one can observe that the histogram for Drug 1 is
somewhat symmetrical while the histogram for Drug 2 is symmetrical and
for Drug 3 is somewhat erratic. In addition, the relative frequency polygons
which are superimposed on the histograms may all be approximated by a
bell shaped distribution. Thus the assumption of sampling from normal
populations does not seem to have been severely violated.