[R] Problems with lm()

[Hsin-Ya Lee]

Dear Dr. Dalgaard

Sorry for delay reply..
That's exactly what I was looking for - thanks a lot.

Hsin-Ya



Peter Dalgaard wrote:
> 
> <oops, this got sent as reply to Andrew only>
> 
> Andrew Robinson wrote:
>> In your data, subject is nested within sequence.  Was that your
>> intention?
>>
>>   
> Presumably yes. This looks like a standard cross-over design.
> 
> I fail to see what the interaction between subject and sequence might
> mean, so I also have no idea what SPSS might have done. (The list does
> not allow .doc attachments).
> 
> Since this is a balanced design, you can get almost the right analysis by
> 
>> m <- lm(Max ~ sequence + subject + period +
> + drug, data=Data)
>> anova(m)
> Analysis of Variance Table
> 
> Response: Max
>            Df Sum Sq Mean Sq F value Pr(>F)
> sequence   1    585     585  0.0160 0.9014
> subject   12 634325   52860  1.4469 0.2660
> period     1  63175   63175  1.7293 0.2131
> drug       1  58149   58149  1.5917 0.2311
> Residuals 12 438395   36533
> 
> in which you have to know that sequence is aliased with the drug:period
> interaction, AND that it needs to be compared with the intersubject
> variation. I.e. the F test is wrong and should be replaced with F=
> 585/52860 = 0.011on 1 and 12 df.
> 
> However, a better way is
> 
>> summary(aov(Max ~ period*drug + Error(subject), data=Data))
> 
> Error: subject
>              Df Sum Sq Mean Sq F value Pr(>F)
> period:drug  1    585     585  0.0111  0.918
> Residuals   12 634325   52860
> 
> Error: Within
>            Df Sum Sq Mean Sq F value Pr(>F)
> period     1  63175   63175  1.7293 0.2131
> drug       1  58149   58149  1.5917 0.2311
> Residuals 12 438395   36533
> 
> 
> 
> -- 
>     O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
>    c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
>   (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907
> 
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> 

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