Re: [R] nested ANCOVA: still confused

From: Jeffrey Stratford <stratja_at_auburn.edu>
Date: Thu 26 Jan 2006 - 10:56:31 EST


Harold, Kingsford, and R-users,

I settled on using the lmer function. I think the memory issue was more a function of my poor coding than an actual memory problem. I also switched the label from "box" to "clutch" to avoid any potential confusion with other functions.

This coding seems to have worked:

> eabl <- lmer(rtot ~ sexv + (purban2|clutch), maxIter=1000, data=bb,
na.action=na.omit)

However, I have two remaining questions: (1)how concerned should I be with the warning message below and (2) is there a way to invoke output to get an estimate of the effect of purban2 (the proportion of urban cover 200 m around a box) on feather color (rtot) and if there is a difference between the sexes? I used the summary function and it doesn't tell me much (see output below).

I'll read up mixed models when Pinheiro arrives but any suggestions for diagnostics? I'm going to repeat this study and expand it by doubling or tripling the number of birds.

Warning message:
nlminb returned message false convergence (8)  in: "LMEoptimize<-"(`*tmp*`, value = list(maxIter = 200, tolerance = 1.49011611938477e-08,

> summary(eabl)

Linear mixed-effects model fit by REML
Formula: rtot ~ sexv + (purban2 | clutch)

   Data: bb

      AIC      BIC    logLik MLdeviance REMLdeviance
 5164.284 6997.864 -2052.142   4128.792     4104.284
Random effects:
 Groups   Name               Variance  Std.Dev. Corr                    
                                                                        
      
 clutch   (Intercept)           502829   709.10                         
                                                                        
      
          purban20             1341990  1158.44 -0.477                  
                                                                        
      
          purban20.006711409   5683957  2384.10 -0.226  0.082           
                                                                        
      
          purban20.01342282    1772922  1331.51 -0.386  0.176  0.067  
.
.
.

.
.
# of obs: 235, groups: clutch, 74

Fixed effects:

            Estimate Std. Error t value
(Intercept)  5950.01     241.59  24.628
sexvm        1509.07     145.73  10.355

Correlation of Fixed Effects:
      (Intr)

sexvm -0.304

Thanks many time over,

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> 01/25/06 6:37 AM >>> OK, we're getting somewhere. First, it looks as though (by the error message) that you have a big dataset. My first recommendation is to use lmer instead of lme, you will see a significant benefit in terms of computional speed.

For the model this would be

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

Now, you have run out of memory. I don't know what operating system you are using, so go and see the appropriate FAQ for increasing memory for your OS.

Second, I made a mistake in my reply. Your random statement should be random=~purban|box/chick denoting that chicks are nested in boxes, not boxes nested in chicks, sorry about that.

Now, why is it that each chick within box has the same value for purban? If this is so, why are you fitting that as a random effect? It seems not to vary across individual chicks, right? It seems there is only an effect of box and not an effect for chicks. Why not just fit a random effect only for box such as:

rtot.lme <- lme(fixed=rtot~sexv, random=~purban2|box, na.action=na.omit,bb)

or in lmer
lmer(rtot ~ sexv + (purban|box), bb, na.action=na.omit)

Harold  

-----Original Message-----

From:	Jeffrey Stratford [mailto:stratja@auburn.edu]
Sent:	Tue 1/24/2006 8:57 PM
To:	Doran, Harold; r-help@stat.math.ethz.ch
Cc:	
Subject:	RE: [R] nested ANCOVA: still confused

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

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

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 Thu Jan 26 11:07:58 2006

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:42:10 EST