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glmer with/without intercept gave different results

6 messages · Chang, Yu-Mei, ONKELINX, Thierry, Jarrod Hadfield

#
Dear Ruby,

The hypotheses of those models are different. Hence the diference in
p-values.

Fit1:
H0: Capsule 1 = 0
H0: Capsule 2 - Capsule 1 = 0
H0: Control - Capsule 1 = 0

Fit2:
H0: Capsule 1 = 0
H0: Capsule 2 = 0
H0: Control = 0

However, the predictions of both model should be the same.

Best regards,

Thierry


------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium

tel. + 32 54/436 185
Thierry.Onkelinx at 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
#
Dear Thierry,

I understood the hypotheses were different between the two models. What
surprise me were the different estimated variances for the random
effects and also the estimated differences between fixed effects levels.


Ruby

-----Original Message-----
From: ONKELINX, Thierry [mailto:Thierry.ONKELINX at inbo.be] 
Sent: 18 November 2010 15:43
To: Chang, Yu-Mei; r-sig-mixed-models at r-project.org
Subject: RE: [R-sig-ME] glmer with/without intercept gave different
results

Dear Ruby,

The hypotheses of those models are different. Hence the diference in
p-values.

Fit1:
H0: Capsule 1 = 0
H0: Capsule 2 - Capsule 1 = 0
H0: Control - Capsule 1 = 0

Fit2:
H0: Capsule 1 = 0
H0: Capsule 2 = 0
H0: Control = 0

However, the predictions of both model should be the same.

Best regards,

Thierry


------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium

tel. + 32 54/436 185
Thierry.Onkelinx at 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
#
Dear Ruby,

I notice that the fixed effect estimates are very small and the Cell  
variance very large which may indicate numerical issues.

What does:

table(table(Cyptoplasmic.vacuolation, Cell)[1,])

look like?

Cheers,

Jarrod
On 18 Nov 2010, at 15:51, Chang, Yu-Mei wrote:

            

  
    
#
Dear Jarrod,

Yes, that's the culprit. The 10 repeated cells are either all 0's or
1's!
0  10 
 37 213

Many thanks! 
Ruby


-----Original Message-----
From: Jarrod Hadfield [mailto:j.hadfield at ed.ac.uk] 
Sent: 18 November 2010 16:09
To: Chang, Yu-Mei
Cc: ONKELINX, Thierry; r-sig-mixed-models at r-project.org
Subject: Re: [R-sig-ME] glmer with/without intercept gave different
results

Dear Ruby,

I notice that the fixed effect estimates are very small and the Cell  
variance very large which may indicate numerical issues.

What does:

table(table(Cyptoplasmic.vacuolation, Cell)[1,])

look like?

Cheers,

Jarrod
On 18 Nov 2010, at 15:51, Chang, Yu-Mei wrote:

            
------------------------------------------------------------------------

  
    
#
Dear Ruby,

I do not think a REML solution exists for the Cell variance in this  
instance (it's infinity). I presume the data for each Cell all have  
the same Villus and Group?  If so you would be better off reducing  
your data to 250 binary data (i.e. One datum for each Cell) and  
removing the (1|Cell) term from the model.

Cheers,

Jarrod
On 18 Nov 2010, at 16:18, Chang, Yu-Mei wrote: