[R] Possible bug

Charles-Édouard Giguère ce@g|guere @end|ng |rom gm@||@com
Thu Mar 17 20:38:14 CET 2022


The plant and Treatment are aliased (if you know the value of plant you know
the value of treatment) so you shouldn't add them together in the same
model. That being said when you enter treatment first and then plant you are
adding the extra information from plant as the second effect and in the
second model when you try to enter treatment as the second effect there's
nothing more to fit. If you look closely at the two model you will notice
that the total variance and the total degree of freedom are the same. Also
when you  use *,  what you are fitting is plant + treatment +
plant:treatment but you don't see the interaction in the model because it is
useless in the model. 


Hope it helps, 



Treatment    Qn1 Qn2 Qn3 Qc1 Qc3 Qc2 Mn3 Mn2 Mn1 Mc2 Mc3 Mc1

  nonchilled   7   7   7   0   0   0   7   7   7   0   0   0

  chilled      0   0   0   7   7   7   0   0   0   7   7   7


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De : R-help <r-help-bounces using r-project.org> De la part de konrad via R-help
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Objet : [R] Possible bug


Dear all,



I recently conducted aov calculations of datasets::CO2.



When I'm using the following code: 

'summary(aov(CO2$uptake~CO2$Treatment*CO2$Plant))'. Everything is fine. 

I get a result for Plant and Treatment.



However, if using: 'summary(aov(CO2$uptake~CO2$Plant*CO2$Treatment))' 

'Treatment' is ignored.


I'm using R 3.6 on Linux Mint. Any idea why this happens?









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