Two Sample Tests - Agricultural Statistical Data Analysis Using Stata - page 71

he response _ var is the dependent variable, which is what is
being measured, while the factor _ var is the independent variable
or the specific treatments. There are several options available with this
command including the ability to produce several multiple-compari-
son tests.
Output and Meaning
Open the dataset virustest.dta. This is a sample dataset of watermelon
plants that were inoculated with zucchini yellow mosaic virus—
Egyptian strain (ZYMV-E). This virus is particularly virulent on
watermelons and was not found in the United States. Because of this,
to prevent this virus from escaping during testing, evaluation was
restricted to a growth chamber. Because growth chambers have very
uniform conditions, the experiment was set up as a CRD of 11 plants
(replications) of each of nine watermelon cultivars.
Enter the following command:
oneway absorb trt
This will result in the following:
Analysis of Variance
Source SS df MS F Prob > F
----------------------------------------------------------------
Between groups 3.12941196 8 .391176495 145.97 0.0000
Within groups .241184086 90 .002679823
----------------------------------------------------------------
Total 3.37059605 98 .034393837
Bartlett's test for equal variances:
chi2(8) = 21.5128 Prob>chi2 = 0.006
The resulting table is called an analysis of variance table. The pre-
sentation of ANOVA calculations in this form is fairly standard across
textbooks and statistical programs. The columns, Source, SS', df ',
MS', F, and Prob > F will be present in all ANOVA tables, but the
number of rows will differ as the experimental designs become more
complex resulting in more complex models. This will become evident
as we look at more complex designs later in the topic.