[R] summary.lme() vs. anova.lme()

[Dimitris Rizopoulos]

Hi Dan,

check the `type' argument of `anova.lme()' which defaults to 
"sequential". This is also discussed in Pinheiro and Bates but I don't 
have the book with me now to trace the page.

I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/396887
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Dan Bebber" <danbebber at forestecology.co.uk>
To: <r-help at stat.math.ethz.ch>
Sent: Wednesday, November 17, 2004 3:35 PM
Subject: [R] summary.lme() vs. anova.lme()


> Dear R list:
>
> I modelled changes in a variable (mconc) over time (d) for 
> individuals
> (replicate) given one of three treatments (treatment) using:
> mconc.lme <- lme(mconc~treatment*poly(d,2), 
> random=~poly(d,2)|replicate,
> data=my.data)
>
> summary(mconc.lme) shows that the linear coefficient of one of the
> treatments is significantly different to zero, viz.
>                            Value Std.Error  DF   t-value p-value
> ...      ... ...      ...
> ...
> treatmentf:poly(d, 2)1  1.3058562 0.5072409 315  2.574430  0.0105
>
> But anova(mconc.lme) gives a non-significant result for the 
> treatment*time
> interaction, viz.
>                     numDF denDF   F-value p-value
> (Intercept)              1   315 159.17267  <.0001
> treatment                2    39   0.51364  0.6023
> poly(d, 2)               2   315  17.43810  <.0001
> treatment:poly(d, 2)     4   315   2.01592  0.0920
>
> Pinheiro & Bates (2000) only discusses anova() for single arguments 
> briefly
> on p.90.
> I would like to know whether these results indicate that the 
> significant
> effect found in summary(mconc.lme) is spurious (perhaps due to
> multiplicity).
>
> Many thanks,
> Dan Bebber
>
> Department of Plant Sciences
> University of Oxford
> South Parks Road
> Oxford OX1 3RB
> UK
> Tel. 01865 275000
>
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