[R] Problems with lm()

Christoph Scherber
Thu, 17 Jul 2008 13:14:07 -0000

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
>
>
> .
>