Statistical
modelling/Milk offtake
GenStat also produces warning messages as appropriate
during the analysis. The messages shown here, which should be read in
conjunction with the scatter diagram on the previous page, were produced when
non-parallel lines were fitted.
* MESSAGE: The following units have large
standardized residuals: |
Unit |
Response |
Residual |
39 |
5.600 |
5.96 |
40 |
4.400 |
3.79 |
* MESSAGE: The error variance does not appear to be constant:
large responses are more variable than small responses
* MESSAGE: The following units have high leverage: |
Unit |
Response |
Leverage |
65 |
1.300 |
0.068 |
67 |
1.600 |
0.068 |
80 |
1.700 |
0.068 |
85 |
2.300 |
0.068 |
etc |
Message 1. The two units have standardised residuals
(calculated as the deviation of an observation from its fitted value divided by
the overall residual standard deviation) meaning that they fall some distance
away from the fitted line and are ´outliers´.
Message 2. This suggests that the assumption the
y-variable has a constant variance may not be tenable.
Message 3. Units with high leverage are those points that
have a strong influence on the direction of the regression line. These points in
this example are those that lie to the extreme right for calves aged 12 months
and beyond.
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