Agriculture Reference
In-Depth Information
The results indicate that there were differences between the varieties
as well as there being a season-by-variety interaction. To see these differ-
ences and the interaction, enter the following command for the results:
table
var season,
contents
(
mean
wt)
-----------------------------------
| Season: 1-spring,
| 2-fall
Variety | Spring Fall
---------------+-------------------
Orange Bulldog | 100.3375 126.6
Longface | .8125 0
Sppktacular | 27.8375 6.375
Spirit | 1.3 8.7
Appalachian | 3.5 39.3
Phantom | .4625 1.925
Trickster | 3.85 1.375
-----------------------------------
Although we did not do any more analysis other than to calculate
the means, I think it is evident that Orange Bulldog has yielded sig-
nificantly more than the other varieties. In addition, the interaction
effect is rather modest.
Another common type of factorial is an evaluation over years. In
this case, the years are not considered a fixed effect as seasons are, but
rather a random effect, as every year can have different environmental
effects. To show this analysis, open the dataset Plum Trial Years.dta
and enter the following command:
anova
yield year
/
rep
|
year var
/
year
#
var
/
rep
#
var
|
year
This results in the following output:
Number of obs = 144 R-squared = 1.0000
Root MSE = 0 Adj R-squared =
Source | Partial SS df MS F Prob > F
--------+----------------------------------------------------
Model | 10961.7903 143 76.6558764
|
year | 719.53614 2 359.76807 4.10 0.0381
rep|year | 1317.46597 15 87.8310646
-------+----------------------------------------------------
var | 656.593453 7 93.7990647 1.10 0.4132
year#var | 1191.44855 14 85.103468
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