[R] degrees of freedom in a LME model
Federico Calboli
f.calboli at ucl.ac.uk
Thu Jun 26 16:57:25 CEST 2003
Dear All,
I am analysing some data for a colleague (not my data, gotta be published
so I cannot divulge).
My response variable is the number of matings observed per day for some
fruitlies.
My factors are:
Day: the observations were taken on 9 days
Regime: 3 selection regimes
Line: 3 replicates per selection regime.
I have 81 observations in total
The lines are coded A to I, so I do not need to do any extra grouping.
my model is:
anova(lme(Matings ~ Day * Regime, random = ~1| Line/Day, mydata))
I would expect to have:
1 df per Day
2 df per Regime
2 df per Day * Regime
6 df per Line %in% Regime
6 df per Day * Line %in% Regime,
so my anova would have:
numDF denDF
int 1 63
Day 1 6
Regime 2 6
D*R 2 6
what I get is:
numDF denDF
int 1 69
Day 1 69
Regime 2 6
D*R 2 69
why is lme not calculating correctly the Line/Day interation ?
I am using R 1.7.0 under W2K, although I updated the packages and I get the
warning "nlme lib built under R1.7.1..."
Regards,
Federico
=========================
Federico C.F. Calboli
Department of Biology
University College London
Room 327
Darwin Building
Gower Street
London
WClE 6BT
Tel: (+44) 020 7679 4395
Fax (+44) 020 7679 7096
f.calboli at ucl.ac.uk
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