Re: [R] Mixed models fixed effects

2009-03-13 Thread ONKELINX, Thierry
Dear Emma,

Have you tried a simpler model? False convergence can be due to an
overcomplex model. Can you give a brief outline of your data? E.g. how
many sites, how many data per site, ... Cross tabulations of all pairs
of factor variables are usefull too.

HTH,

Thierry 




ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
thierry.onkel...@inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-Oorspronkelijk bericht-
Van: Emma Stone [mailto:emma.st...@bristol.ac.uk] 
Verzonden: vrijdag 13 maart 2009 10:50
Aan: ONKELINX, Thierry; Emma Stone; r-help@r-project.org
Onderwerp: RE: [R] Mixed models fixed effects

Hi Thierry,

That's great thanks!

I have done as you have said but I keep getting a warning message here
is 
my code:

G1Hvol-glmer(passes~hvolume+style+habitat(1|Site),family = poisson)

And this is the message i get:
Warning message:
In mer_finalize(ans) : false convergence (8)

any ideas??

Emma


--On 11 March 2009 15:45 +0100 ONKELINX, Thierry 
thierry.onkel...@inbo.be wrote:

 Hi Emma,

 Continuous predictors are no problem at all. You can mix both
continuous
 and categorial predictors if needed. I suppose your response are
counts
 (the number of bats that passes)? In that case a generalised linear
 mixed model is more appropriate. With the lme4 package you could try
 something like this:

 library(lme4)
 Model - glmer(BatPasses ~ Width + Height + (1|Site), family =
poisson)

 HTH,

 Thierry

 PS There is a mailing list dedicated to mixed models:
R-Sig-MixedModels


 
 ir. Thierry Onkelinx
 Instituut voor natuur- en bosonderzoek / Research Institute for Nature
 and Forest
 Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
 methodology and quality assurance
 Gaverstraat 4
 9500 Geraardsbergen
 Belgium
 tel. + 32 54/436 185
 thierry.onkel...@inbo.be
 www.inbo.be

 To call in the statistician after the experiment is done may be no
more
 than asking him to perform a post-mortem examination: he may be able
to
 say what the experiment died of.
 ~ Sir Ronald Aylmer Fisher

 The plural of anecdote is not data.
 ~ Roger Brinner

 The combination of some data and an aching desire for an answer does
not
 ensure that a reasonable answer can be extracted from a given body of
 data.
 ~ John Tukey

 -Oorspronkelijk bericht-
 Van: r-help-boun...@r-project.org
[mailto:r-help-boun...@r-project.org]
 Namens Emma Stone
 Verzonden: woensdag 11 maart 2009 15:29
 Aan: r-help@r-project.org
 Onderwerp: Re: [R] Mixed models fixed effects

 Dear All,

 This may sound like a dumb question but I am trying to use a mixed
model
 to
 determine the predictors of bat activity along hedges within 8 sites.
So
 my
 response is continuous (bat passes) my predictors fixed effects are
 continuous (height metres), width (metres) etc and the random effect
is
 site  - can you tell me if the fixed effects can be continuous as all
 the
 examples I have read show them as categorical, but this is not covered
 in
 any documents I can find.

 Help!

 Emma

 __
 R-help@r-project.org mailing list
 https://stat.ethz.ch/mailman/listinfo/r-help
 PLEASE do read the posting guide
 http://www.R-project.org/posting-guide.html
 and provide commented, minimal, self-contained, reproducible code.

 Dit bericht en eventuele bijlagen geven enkel de visie van de
schrijver
 weer  en binden het INBO onder geen enkel beding, zolang dit bericht
niet
 bevestigd is door een geldig ondertekend document. The views expressed
in
 this message  and any annex are purely those of the writer and may not
be
 regarded as stating  an official position of INBO, as long as the
message
 is not confirmed by a duly  signed document.



--
Emma Stone
Postgraduate Researcher
Bat Ecology and Bioacoustics Lab
 Mammal Research Unit
School of Biological Sciences,
University of Bristol, Woodland Road,
Bristol, BS8 1UG
Email: emma.st...@bristol.ac.uk



Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer 
en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is
door een geldig ondertekend document. The views expressed in  this message 
and any annex are purely those of the writer and may

Re: [R] Mixed models fixed effects

2009-03-13 Thread Emma Stone
0.00 1447.68
37   140.00 1405.89
38   430.00  393.62
39   410.00  461.28
40   410.00  290.35
41   14 1275.61 5695.19
42   12   60.61 3502.27
43   11  129.36 2962.34
44   13   19.95 3786.72
45   110.00 1303.16
46   130.00 1044.52
47   120.00  461.22
48   140.00  363.79


--On 13 March 2009 11:01 +0100 ONKELINX, Thierry 
thierry.onkel...@inbo.be wrote:



Dear Emma,

Have you tried a simpler model? False convergence can be due to an
overcomplex model. Can you give a brief outline of your data? E.g. how
many sites, how many data per site, ... Cross tabulations of all pairs
of factor variables are usefull too.

HTH,

Thierry




ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
thierry.onkel...@inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-Oorspronkelijk bericht-
Van: Emma Stone [mailto:emma.st...@bristol.ac.uk]
Verzonden: vrijdag 13 maart 2009 10:50
Aan: ONKELINX, Thierry; Emma Stone; r-help@r-project.org
Onderwerp: RE: [R] Mixed models fixed effects

Hi Thierry,

That's great thanks!

I have done as you have said but I keep getting a warning message here
is
my code:

G1Hvol-glmer(passes~hvolume+style+habitat(1|Site),family = poisson)

And this is the message i get:
Warning message:
In mer_finalize(ans) : false convergence (8)

any ideas??

Emma


--On 11 March 2009 15:45 +0100 ONKELINX, Thierry
thierry.onkel...@inbo.be wrote:


Hi Emma,

Continuous predictors are no problem at all. You can mix both

continuous

and categorial predictors if needed. I suppose your response are

counts

(the number of bats that passes)? In that case a generalised linear
mixed model is more appropriate. With the lme4 package you could try
something like this:

library(lme4)
Model - glmer(BatPasses ~ Width + Height + (1|Site), family =

poisson)


HTH,

Thierry

PS There is a mailing list dedicated to mixed models:

R-Sig-MixedModels






ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
thierry.onkel...@inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no

more

than asking him to perform a post-mortem examination: he may be able

to

say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does

not

ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-Oorspronkelijk bericht-
Van: r-help-boun...@r-project.org

[mailto:r-help-boun...@r-project.org]

Namens Emma Stone
Verzonden: woensdag 11 maart 2009 15:29
Aan: r-help@r-project.org
Onderwerp: Re: [R] Mixed models fixed effects

Dear All,

This may sound like a dumb question but I am trying to use a mixed

model

to
determine the predictors of bat activity along hedges within 8 sites.

So

my
response is continuous (bat passes) my predictors fixed effects are
continuous (height metres), width (metres) etc and the random effect

is

site  - can you tell me if the fixed effects can be continuous as all
the
examples I have read show them as categorical, but this is not covered
in
any documents I can find.

Help!

Emma

__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Dit bericht en eventuele bijlagen geven enkel de visie van de

schrijver

weer  en binden het INBO onder geen enkel beding, zolang dit bericht

niet

bevestigd is door een geldig ondertekend document. The views expressed

in

this message  and any annex are purely those of the writer and may not

be

regarded as stating  an official position of INBO, as long as the

message

is not confirmed by a duly  signed document.




--
Emma Stone
Postgraduate Researcher
Bat Ecology

Re: [R] Mixed models fixed effects

2009-03-13 Thread ONKELINX, Thierry
Dear Emma,

First of all make shure that style and habitat are factors (assuming
that they are categorical).

glmer(passes~hvolume+style+habitat(1|Site),family = poisson)

Style has 3 levels, habitat 5 levels. So your model needs to estimate 1
parameter for hvolume, 2 for style, 4 for habitat and 1 for site. In
total 8 parameters. A rule of thumbs tells you that you need about 10
samples for each parameter. Hence you dataset (n = 48) is to small for
this kind of model.

Aditionally the variable habitat has some rare levels. Only one occures
of levels 3 and 5, and just a few more for levels 2 and 4. This kind of
data won't give you reliable estimates for habitat. So I would suggest
to drop this from your model.

HTH,

Thierry 




ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
thierry.onkel...@inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-Oorspronkelijk bericht-
Van: Emma Stone [mailto:emma.st...@bristol.ac.uk] 
Verzonden: vrijdag 13 maart 2009 11:08
Aan: ONKELINX, Thierry; Emma Stone; r-help@r-project.org
Onderwerp: RE: [R] Mixed models fixed effects

Hi Thierry,

Thanks, my data are pasted in below: n = 48, with different numbers if
site 
replicates.

   Site passes length width height ohwidth ohheight style shape nogap
pgaps
1 1 32  38.21  7.18   2.600.00 0.00 1 1 0
0.00
2 1  7 154.38  2.55   2.430.00 0.00 2 1 0
0.00
3 2 24 130.00  2.73   4.965.83 2.27 1 2 0
1.92
4 2 43 130.00  2.73   4.963.45 2.45 1 2 0
1.91
5 2 32 130.00  3.30   4.343.67 2.63 3 2 0
0.00
6 2  9 130.00  3.30   4.342.13 1.53 2 2 0
0.00
7 2 25 214.00  1.65   6.232.80 2.53 3 2 0
0.00
8 2  1 214.00  2.20   1.050.00 0.00 2 1 0
0.00
9 2 57 188.00  5.87   4.973.23 2.13 2 2 0
0.00
102 32 211.00  2.63   6.094.37 2.50 2 2 0
0.00
112 14 211.00  2.63   6.093.50 2.53 2 2 0
0.00
123 78 192.00  2.30   2.400.33 0.88 2 2 0
2.19
133 11 192.00  2.50   2.500.13 0.55 2 2 0
2.19
143  9 444.00  2.10   1.930.00 0.00 2 1 2
6.19
154 40  44.00  1.83   2.050.00 0.00 1 1 1
31.81
164112  44.00  1.58   1.730.00 0.00 1 1 1
31.81
174 23  98.00  2.18   1.700.00 0.00 1 3 0
2.55
184 23  98.00  1.78   1.600.00 0.00 1 1 0
2.55
194  4  84.00  1.73   1.980.00 0.00 1 3 1
17.02
204 72  88.00  3.30   5.303.30 1.45 1 2 0
0.00
215207 116.00  3.08   3.383.65 3.68 1 2 0
0.00
225  2 116.00  2.85   2.183.18 3.53 1 2 0
0.00
235 81 104.00  2.68   2.781.00 0.75 2 1 0
0.00
245  3 104.00  2.68   2.380.00 0.00 2 1 0
0.00
255 21  59.00  2.78   4.032.23 1.75 2 2 0
6.78
265  1  59.00  2.78   3.331.38 1.35 2 2 0
6.78
276 82 165.56  2.50   4.001.00 1.33 1 2 0
0.00
286  1 165.56  2.60   3.630.50 1.40 1 2 0
0.00
296 46  69.35  3.23  10.674.73 4.67 1 2 0
0.00
306  7 165.56  3.50  10.172.67 1.67 1 2 0
0.00
316 45 136.00  3.33   3.670.00 0.00 1 2 0
2.20
326  3 136.00  3.33   2.750.00 0.00 1 2 0
3.30
336 34  82.00  2.83  12.003.33 3.83 1 2 0
0.00
347  0 228.00  2.57   2.700.30 1.00 2 2 0
0.50
357148 228.00  3.08   4.680.75 1.75 2 2 0
0.05
367  0 208.00  2.40   2.900.00 0.00 2 1 0
1.44
377 38 208.00  2.57   2.630.00 0.00 2 1 0
1.44
387  0 112.00  2.13   1.650.00 0.00 2 1 0
0.50
397  0 192.00  1.55   1.550.00 0.00 2 1 0
0.00
407  0 132.00  1.56   1.410.00 0.00 2 1 0
0.00
418 52 148.00  5.05   7.622.55

Re: [R] Mixed models fixed effects

2009-03-13 Thread Emma Stone

Hi Thierry,

Thanks again! You are a great help!!

I have taken habitat out, and then run it with style but still the same 
problem exists, so I have taken both style and habitat out. The problem 
here is it leaves me with only 3 parameters and because they are all 
correlated I cant use them in the same models, so I just have 3 single 
models (one for each parameter) - which isnt ideal.


G3Pgaps-glmer(passes~pgaps+(1|Site),family=poisson)
C1Hvol-glmer(passes~hvolume+(1|Site))
C2OHArea-glmer(passes~oharea+(1|Site))

Also, when I run the C1 and C2 model, it wont work if I state family 
poisson.


Is there anyway I can get rid of the correlations in the parameters so that 
I can use them in the same model? Or is there another option to boost n, ie 
bootsrapping??


Thanks again

Emma

--On 13 March 2009 11:21 +0100 ONKELINX, Thierry 
thierry.onkel...@inbo.be wrote:



poisson




--
Emma Stone
Postgraduate Researcher
Bat Ecology and Bioacoustics Lab
 Mammal Research Unit
School of Biological Sciences,
University of Bristol, Woodland Road,
Bristol, BS8 1UG
Email: emma.st...@bristol.ac.uk

__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.


Re: [R] Mixed models fixed effects

2009-03-11 Thread Emma Stone

Dear All,

This may sound like a dumb question but I am trying to use a mixed model to 
determine the predictors of bat activity along hedges within 8 sites. So my 
response is continuous (bat passes) my predictors fixed effects are 
continuous (height metres), width (metres) etc and the random effect is 
site  - can you tell me if the fixed effects can be continuous as all the 
examples I have read show them as categorical, but this is not covered in 
any documents I can find.


Help!

Emma

__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.


Re: [R] Mixed models fixed effects

2009-03-11 Thread ONKELINX, Thierry
Hi Emma,

Continuous predictors are no problem at all. You can mix both continuous
and categorial predictors if needed. I suppose your response are counts
(the number of bats that passes)? In that case a generalised linear
mixed model is more appropriate. With the lme4 package you could try
something like this:

library(lme4)
Model - glmer(BatPasses ~ Width + Height + (1|Site), family = poisson)

HTH,

Thierry

PS There is a mailing list dedicated to mixed models: R-Sig-MixedModels


ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
thierry.onkel...@inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-Oorspronkelijk bericht-
Van: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org]
Namens Emma Stone
Verzonden: woensdag 11 maart 2009 15:29
Aan: r-help@r-project.org
Onderwerp: Re: [R] Mixed models fixed effects

Dear All,

This may sound like a dumb question but I am trying to use a mixed model
to 
determine the predictors of bat activity along hedges within 8 sites. So
my 
response is continuous (bat passes) my predictors fixed effects are 
continuous (height metres), width (metres) etc and the random effect is 
site  - can you tell me if the fixed effects can be continuous as all
the 
examples I have read show them as categorical, but this is not covered
in 
any documents I can find.

Help!

Emma

__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer 
en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is
door een geldig ondertekend document. The views expressed in  this message 
and any annex are purely those of the writer and may not be regarded as stating 
an official position of INBO, as long as the message is not confirmed by a duly 
signed document.

__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.


Re: [R] Mixed models fixed effects

2009-03-11 Thread Simon Pickett

Also check out these pdfs
http://cran.r-project.org/other-docs.html

and try to get your hands on the bible
http://www.amazon.co.uk/R-Book-Michael-J-Crawley/dp/0470510242

Simon.






Hi Emma,

Continuous predictors are no problem at all. You can mix both continuous
and categorial predictors if needed. I suppose your response are counts
(the number of bats that passes)? In that case a generalised linear
mixed model is more appropriate. With the lme4 package you could try
something like this:

library(lme4)
Model - glmer(BatPasses ~ Width + Height + (1|Site), family = poisson)

HTH,

Thierry

PS There is a mailing list dedicated to mixed models: R-Sig-MixedModels


ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
thierry.onkel...@inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-Oorspronkelijk bericht-
Van: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org]
Namens Emma Stone
Verzonden: woensdag 11 maart 2009 15:29
Aan: r-help@r-project.org
Onderwerp: Re: [R] Mixed models fixed effects

Dear All,

This may sound like a dumb question but I am trying to use a mixed model
to
determine the predictors of bat activity along hedges within 8 sites. So
my
response is continuous (bat passes) my predictors fixed effects are
continuous (height metres), width (metres) etc and the random effect is
site  - can you tell me if the fixed effects can be continuous as all
the
examples I have read show them as categorical, but this is not covered
in
any documents I can find.

Help!

Emma

__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver 
weer
en binden het INBO onder geen enkel beding, zolang dit bericht niet 
bevestigd is

door een geldig ondertekend document. The views expressed in  this message
and any annex are purely those of the writer and may not be regarded as 
stating
an official position of INBO, as long as the message is not confirmed by a 
duly

signed document.

__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html

and provide commented, minimal, self-contained, reproducible code.



__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.


Re: [R] Mixed models fixed effects

2009-03-11 Thread Mark Difford

Hi Simon,

Carefull, someone is likely to tell you that the bible is Pinheiro, J.C.,
and Bates, D.M. (2000) Mixed-Effects Models in S and S-PLUS, Springer, and
that would be much closer to being correct. Others might mention something
by Searle. Nothing against Crawley, of course. But it usually is better to
get close to the source, and to the active researchers in the field. One
nice thing about the first reference (there are many others) is that Prof.
Bates is an active contributor to this list and to the SIG mixed-models list
(which he maintains):

https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models

Check it out.

Regards, Mark.


Simon Pickett-4 wrote:
 
 Also check out these pdfs
 http://cran.r-project.org/other-docs.html
 
 and try to get your hands on the bible
 http://www.amazon.co.uk/R-Book-Michael-J-Crawley/dp/0470510242
 
 Simon.
 
 
 
 
 
 Hi Emma,

 Continuous predictors are no problem at all. You can mix both continuous
 and categorial predictors if needed. I suppose your response are counts
 (the number of bats that passes)? In that case a generalised linear
 mixed model is more appropriate. With the lme4 package you could try
 something like this:

 library(lme4)
 Model - glmer(BatPasses ~ Width + Height + (1|Site), family = poisson)

 HTH,

 Thierry

 PS There is a mailing list dedicated to mixed models: R-Sig-MixedModels
 
 
 ir. Thierry Onkelinx
 Instituut voor natuur- en bosonderzoek / Research Institute for Nature
 and Forest
 Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
 methodology and quality assurance
 Gaverstraat 4
 9500 Geraardsbergen
 Belgium
 tel. + 32 54/436 185
 thierry.onkel...@inbo.be
 www.inbo.be

 To call in the statistician after the experiment is done may be no more
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 -Oorspronkelijk bericht-
 Van: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org]
 Namens Emma Stone
 Verzonden: woensdag 11 maart 2009 15:29
 Aan: r-help@r-project.org
 Onderwerp: Re: [R] Mixed models fixed effects

 Dear All,

 This may sound like a dumb question but I am trying to use a mixed model
 to
 determine the predictors of bat activity along hedges within 8 sites. So
 my
 response is continuous (bat passes) my predictors fixed effects are
 continuous (height metres), width (metres) etc and the random effect is
 site  - can you tell me if the fixed effects can be continuous as all
 the
 examples I have read show them as categorical, but this is not covered
 in
 any documents I can find.

 Help!

 Emma

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