Sure it does, but still struggling with what is going on...
Thanks
John
________________________________
From:David Winsemius <dwinsem...@comcast.net>
To:David Winsemius <dwinsem...@comcast.net>
oject.org>
Sent:Monday, November 7, 2011 10:27 PM
Subject:Re: [R] why NA coefficients
But this output suggests there may be alligators in the swamp:
> predict(lmod, newdata=data.frame(treat=1, group=2))
1
0.09133691
Warning message:
In predict.lm(lmod, newdata = data.frame(treat = 1, group = 2)) :
prediction from a rank-deficient fit may be misleading
--David.
>
> --David.
>>
>> Thanks
>>
>> John
>>
>>
>> From: David Winsemius <dwinsem...@comcast.net>
>> Cc: "r-help@r-project.org" <r-help@r-project.org>
>> Sent: Monday, November 7, 2011 5:13 PM
>> Subject: Re: [R] why NA coefficients
>>
>>
>> On Nov 7, 2011, at 7:33 PM, array chip wrote:
>>
>> > Hi, I am trying to run ANOVA with an interaction term on 2 factors (treat
>> > has 7 levels, group has 2 levels). I found the coefficient for the last
>> > interaction term is always 0, see attached dataset and the code below:
>> >
>> >> test<-read.table("test.txt",sep='\t',header=T,row.names=NULL)
>> >> lm(y~factor(treat)*factor(group),test)
>> >
>> > Call:
>> > lm(formula = y ~ factor(treat) * factor(group), data = test)
>> >
>> > Coefficients:
>> > (Intercept) factor(treat)2
>> >factor(treat)3
>> > 0.429244 0.499982
>> > 0.352971
>> > factor(treat)4 factor(treat)5
>> >factor(treat)6
>> > -0.204752 0.142042
>> > 0.044155
>> > factor(treat)7 factor(group)2
>> >factor(treat)2:factor(group)2
>> > -0.007775 -0.337907
>> > -0.208734
>> > factor(treat)3:factor(group)2 factor(treat)4:factor(group)2
>> > factor(treat)5:factor(group)2
>> > -0.195138 0.800029
>> > 0.227514
>> > factor(treat)6:factor(group)2 factor(treat)7:factor(group)2
>> > 0.331548 NA
>> >
>> >
>> > I guess this is due to model matrix being singular or collinearity among
>> > the matrix columns? But I can't figure out how the matrix is singular in
>> > this case? Can someone show me why this is the case?
>>
>> Because you have no cases in one of the crossed categories.
>>
>> --David Winsemius, MD
>> West Hartford, CT
>>
>>
>>
>
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> R-help@r-project.orgmailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
