Statistical modelling
We can fit the model by using the dialog box shown below obtained by
Stats → Regression Analysis → Generalized Linear Models... Then by clicking the Options button,
then ticking Accumulated, an analysis of
variance is shown which gives the sums of squares accounted for by each parameter in the model.
Notice first that the first level for each factor (i.e.
those with discrete levels) is omitted. Each parameter estimate represents the
deviation of the level of the factor it represents from the first. Thus, breed
DR lambs have an average weaning weight 0.493 kg less than breed DD lambs, when
adjusted for other fixed effects in the model. This difference in weaning weight
has a standard error of 0.306 kg. The absolute Student's t-value of 1.61 is less than 2,
the approximate value that t needs to exceed to be significant (P<0.05). In
contrast the parameter estimate for RR lambs is statistically significant (absolute t ≥ 2).
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***** Regression Analysis *****
Response variate: WEANWT
Fitted terms: Constant
+ GENOTYPE + YEAR +
SEX + AGEWEAN + DAMAGE7
*** Estimates of parameters
***
Parameter
|
estimate
|
s.e.
|
t
|
Constant
|
4.327
|
0.883
|
4.90
|
GENOTYPE DR
|
-0.493
|
0.306
|
-1.61
|
GENOTYPE RD
|
-0.408
|
0.222
|
-1.84
|
GENOTYPE RR
|
-1.008
|
0.272
|
-3.71
|
YEAR 92
|
-1.551
|
0.308
|
-5.03
|
YEAR 93
|
-1.228
|
0.291
|
-4.22
|
YEAR 94
|
-2.983
|
0.388
|
-7.69
|
YEAR 95
|
-3.258
|
0.346
|
-9.40
|
YEAR 96
|
-2.333
|
0.423
|
-5.51
|
SEX M
|
0.482
|
0.170
|
2.84
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AGEWEAN
|
0.07058
|
0.00886
|
7.97
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DAMAGE7 3
|
1.833
|
0.319
|
5.75
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DAMAGE7 4
|
2.741
|
0.331
|
8.28
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DAMAGE7 5
|
2.742
|
0.322
|
8.52
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DAMAGE7 6
|
2.322
|
0.382
|
6.07
|
DAMAGE7 7
|
1.754
|
0.462
|
3.79
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DAMAGE7 >=8
|
1.405
|
0.647
|
2.17
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*** Accumulated analysis of variance ***
Change |
d.f. |
s.s. |
m.s. |
v.r. |
+GENOTYPE |
3 |
570.427 |
190.142 |
38.68 |
+YEAR |
5 |
735.646 |
147.129 |
29.93 |
+SEX |
1 |
59.013 |
59.013 |
12.00 |
+AGEWEAN |
1 |
336.792 |
336.792 |
68.51 |
+DAMAGE7 |
6 |
445.076 |
74.179 |
15.09 |
Residual |
683 |
3357.495 |
4.916 |
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Total |
699 |
5504.450 |
7.875 |
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