Agriculture Reference
In-Depth Information
The first command (
anova
) generates the typical ANOVA table.
he second command (
pwcompare
entry
,
pveffects
) makes
all pairwise comparisons between the varieties (
entry
), and the
option
pveffects
indicates that the effects table should show the
p values for the comparisons. The p values are listed in the last col-
umn where we can see that the first variety is different from varieties
4 and 5, but not different from varieties 2 and 3. The
pwcompare
command offers several other methods of computing a multiple range
test. Each uses a different approach, which is discussed more fully
later in the chapter. For example, enter the following command and
see the output:
pwcompare
entry,
pveffects tukey
Pairwise comparisons of marginal linear predictions
Margins : asbalanced
---------------------------
| Number of
| Comparisons
-------------+-------------
entry | 10
---------------------------
-----------------------------------------------------
| Tukey
| Contrast Std. Err. t P>|t|
-------------+---------------------------------------
entry |
2 vs 1 | 78.65 64.01717 1.23 0.737
3 vs 1 | -10.40599 64.01717 -0.16 1.000
4 vs 1 | -372.438 64.01717 -5.82 0.003
5 vs 1 | -339.768 64.01717 -5.31 0.005
3 vs 2 | -89.05599 64.01717 -1.39 0.649
4 vs 2 | -451.088 64.01717 -7.05 0.001
5 vs 2 | -418.418 64.01717 -6.54 0.001
4 vs 3 | -362.032 64.01717 -5.66 0.003
5 vs 3 | -329.362 64.01717 -5.14 0.006
5 vs 4 | 32.67 64.01717 0.51 0.984
-----------------------------------------------------
The results between the unadjusted and Tukey's probabilities are
similar. The same pairs of variety means are declared significant in
each test (P<0.05). This will not always be the case, however, and can
be seen by the different probabilities listed. For example, the first
row (2 vs. 1) in the unadjusted comparison has a probability (P>|t|) of
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