[R] Problems with lm()
Christoph Scherber
Christoph.Scherber at agr.uni-goettingen.de
Thu Jul 17 15:14:07 CEST 2008
Dear Hsin-Ya,
The problem here is that subject is a factor with 14 levels, and sequence again is a factor with 2
levels; so the subject:sequence interaction already uses up another (13*1)=13 d.f.; given that there
are only 28 replicates, it is not surprising that there are no residual degrees of freedom left!
What do you intend to test with your model? Maybe I can be of help to solve the problem
Best wishes
Christoph
leeznar at yahoo.com.tw schrieb:
> Dear Dr. Christoph:
>
> Thanks for your reply. I am sure that I use the same data to run GLM with SPSS, but SPSS seems work!!
> I also try your suggestion. I change the sequence data.
> a<-c(1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14)
> b<-c(1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2)
> c<-c(2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2)
> d<-c(2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1)
> d<-c(1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1)
> e<-c(1739,1633,1481,1837,1780,2073,1374,1629,1555,1385,1756,1522,1566,1643,1939,
> 1615,1475,1759,1388,1483,1127,1682,1542,1247,1235,1605,1598,1718 )
> KK<-data.frame(subject=as.factor(a), drug=as.factor(b), period=as.factor(c), sequence=as.factor(d), Max=e)
> lm3<- lm(Max ~ subject*sequence + period + drug+sequence , data=KK)
> print(lm3)
> anova(lm3)
>
> However, it can not work!!
> So, where is the problems? Do I misunderstand what you mean?
>
>
> Best regards,
> Hsin-Ya
>
>
> Dr. Christoph Scherber wrote:
>> Dear Hsin-Ya Lee,
>>
>> The problem seems to be that every subject always only received one
>> sequence:
>>
>> sequence
>> subject 1 2
>> 1 0 2
>> 2 2 0
>> 3 0 2
>> 4 2 0
>> 5 0 2
>> 6 2 0
>> 7 0 2
>> 8 2 0
>> 9 0 2
>> 10 2 0
>> 11 0 2
>> 12 2 0
>> 13 0 2
>> 14 2 0
>>
>>
>> You should try to use a design where each subject receives each of the two
>> sequences. Otherwise
>> obviously the interactions will be not available.
>>
>> Best wishes
>> Christoph
>>
>>
>>
>>
>> leeznar schrieb:
>>> Dear R-users:
>>>
>>> I am a new R-user and I have a question about lm
>>> function. Here is my data.
>>> a<-c(1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14)
>>> b<-c(1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2,1,2)
>>> c<-c(2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2)
>>> d<-c(2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1,2,2,1,1)
>>> e<-c(1739,1633,1481,1837,1780,2073,1374,1629,1555,1385,1756,1522,1566,1643,1939,1615,1475,1759,1388,1483,1127,1682,1542,1247,1235,1605,1598,1718
>>> )
>>> Data<-data.frame(subject=as.factor(a),
>>> drug=as.factor(b), period=as.factor(c),
>>> sequence=as.factor(d), Max=e)
>>>
>>> lm3<- lm(Max ~subject*sequence + sequence + period +
>>> drug, data=Data)
>>> print(lm3)
>>> anova(lm3)
>>>
>>> When I use lm to fit the data, there are some problems
>>> in "subject*sequence". I have use GLM in SPSS to
>>> fit the same data, and it seems there is no problem.
>>>
>>> I don't know where my problem is. How can I get the
>>> same result with SPSS? How can I do?
>>>
>>> Best regards,
>>> Hsin-Ya Lee
>>>
>>>
>>>
>>>
>>>
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>> ______________________________________________
>> R-help at 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.
>>
>>
> Quoted from:
> http://www.nabble.com/Problems-with-lm%28%29-tp17999900p18000246.html
>
>
> .
>
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