Re: [R] nested ANCOVA: still confused

From: Jeffrey Stratford <stratja_at_auburn.edu>
Date: Wed 25 Jan 2006 - 12:57:49 EST


R-users and Harold.

First, thanks for the advice; I'm almost there.

The code I'm using now is

library(nlme)
bb <- read.csv("E:\\eabl_feather04.csv", header=TRUE) bb$sexv <- factor(bb$sexv)
rtot.lme <- lme(fixed=rtot~sexv, random=~purban2|chick/box, na.action=na.omit, data=bb)

A sample of the data looks like this

box	chick	rtot	purban2	sexv
1	1	6333.51	0.026846	f
1	2	8710.884	0.026846	m
2	1	5810.007	0.161074	f
2	2	5524.33	0.161074	f
2	3	4824.474	0.161074	f
2	4	5617.641	0.161074	f
2	5	6761.724	0.161074	f
4	1	7569.673	0.208054	m
4	2	7877.081	0.208054	m
4	4	7455.55	0.208054	f
7	1	5408.287	0.436242	m
10	1	6991.727	0.14094	f
12	1	8590.207	0.134228	f
12	2	7536.747	0.134228	m
12	3	5145.342	0.134228	m
12	4	6853.628	0.134228	f
15	1	8048.717	0.033557	m
15	2	7062.196	0.033557	m
15	3	8165.953	0.033557	m
15	4	8348.58	0.033557	m
16	2	6534.775	0.751678	m
16	3	7468.827	0.751678	m
16	4	5907.338	0.751678	f
21	1	7761.983	0.221477	m
21	2	6634.115	0.221477	m
21	3	6982.923	0.221477	m
21	4	7464.075	0.221477	m
22	1	6756.733	0.281879	f
23	2	8231.496	0.134228	m

The error I'm getting is

Error in logLik.lmeStructInt(lmeSt, lmePars) :

        Calloc could not allocate (590465568 of 8) memory In addition: Warning messages:
1: Fewer observations than random effects in all level 2 groups in: lme.formula(fixed = rtot ~ sexv, random = ~purban2 | chick/box, 2: Reached total allocation of 382Mb: see help(memory.size)

There's nothing "special" about chick 1, 2, etc. These were simply the order of the birds measured in each box so chick 1 in box 1 has nothing to do with chick 1 in box 2.

Many thanks,

Jeff



Jeffrey A. Stratford, Ph.D.
Postdoctoral Associate
331 Funchess Hall
Department of Biological Sciences
Auburn University
Auburn, AL 36849
334-329-9198
FAX 334-844-9234
http://www.auburn.edu/~stratja

>>> "Doran, Harold" <HDoran@air.org> 01/24/06 2:04 PM >>>
Dear Jeff:

I see the issues in your code and have provided what I think will solve your problem. It is often much easier to get help on this list when you provide a small bit of data that can be replicated and you state what the error messages are that you are receiving. OK, with that said, here is what I see. First, you do not need to use the syntax bb$sex in your model, this can be significantly simplified. Second, you do not have a random statement in your model.

Here is your original model:
lme(bb$rtot~bb$sex, bb$purban|bb$chick/bb$box, na.action=na.omit)

Here is what it should be:

lme(fixed = rtot~sex, random=~purban|chick/box, na.action=na.omit, data=bb)

Notice there is a fixed and random call. You can simplify this as

lme(rtot~sex, random=~purban|chick/box, na.action=na.omit, bb)

Note, you can eliminate the "fixed=" portion but not the random statement.

Last, if you want to do this in lmer, the newer function for mixed models in the Matrix package, you would do

lmer(rtot~sex + (purban|box:chick) + (purban|box), na.action=na.omit, data=bb)

Hope this helps.
Harold

-----Original Message-----
From: r-help-bounces@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Jeffrey Stratford Sent: Tuesday, January 24, 2006 11:34 AM To: r-help@stat.math.ethz.ch
Subject: [R] nested ANCOVA: still confused

Dear R-users,

I did some more research and I'm still not sure how to set up an ANCOVA with nestedness. Specifically I'm not sure how to express chicks nested within boxes. I will be getting Pinheiro & Bates (Mixed Effects Models in S and S-Plus) but it will not arrive for another two weeks from our interlibrary loan.

The goal is to determine if there are urbanization (purban) effects on chick health (rtot) and if there are differences between sexes (sex) and the effect of being in the same clutch (box).

The model is rtot = sex + purban + (chick)box.

I've loaded the package lme4. And the code I have so far is

bb <- read.csv("C:\\eabl\\eabl_feather04.csv", header=TRUE) bb$sex <- factor(bb$sex) rtot.lme <- lme(bb$rtot~bb$sex, bb$purban|bb$chick/bb$box,
na.action=na.omit)

but this is not working.

Any suggestions would be greatly appreciated.

Thanks,

Jeff



Jeffrey A. Stratford, Ph.D.
Postdoctoral Associate
331 Funchess Hall
Department of Biological Sciences
Auburn University
Auburn, AL 36849
334-329-9198
FAX 334-844-9234
http://www.auburn.edu/~stratja

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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Jan 25 13:08:22 2006

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