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st: RE: Xtpoisson and quadchk


From   "Jesper Lindhardsen" <[email protected]>
To   <[email protected]>
Subject   st: RE: Xtpoisson and quadchk
Date   Tue, 22 Mar 2011 08:45:33 +0100

Hi Garry,

My guess is that it has something to do with how you defined/created
your 'service' variable as it is indeed your offset if I understand your
model correctly (exposure(service) = offset(ln(service)) - see help
-xtpoisson-).
HTH,
Jesper


Jesper Lindhardsen
MD, PhD candidate
Department of Cardiovascular Research
Copenhagen University Hospital, Gentofte
Denmark



-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Garry
Anderson
Sent: 22 March 2011 08:31
To: [email protected]
Subject: st: Xtpoisson and quadchk

Dear Statalisters,

The message after the -quadchk- command seems a little strange. 
The message is

Refitting model intpoints() =  8
factor variables and time-series operators not allowed
in option offset()
error refitting model
r(101);

I do not think I am using a factor variable nor a time-series operator,
and I am not using the offset option.

Any ideas as to the meaning of this message would be appreciated.




. use http://www.stata-press.com/data/r11/ships,clear

. xtpoisson accident op_75_79 co_65_69 co_70_74 co_75_79,
exposure(service) irr normal

Fitting comparison Poisson model:

Iteration 0:   log likelihood = -147.37993  
Iteration 1:   log likelihood = -80.372714  
Iteration 2:   log likelihood = -80.116093  
Iteration 3:   log likelihood = -80.115916  
Iteration 4:   log likelihood = -80.115916  

Fitting full model:

tau =  0.0     log likelihood = -80.115916
tau =  0.1     log likelihood = -76.060792
tau =  0.2     log likelihood = -77.535639

Iteration 0:   log likelihood = -76.360754  
Iteration 1:   log likelihood = -75.585665  
Iteration 2:   log likelihood = -74.788481  
Iteration 3:   log likelihood = -74.780993  
Iteration 4:   log likelihood = -74.780982  
Iteration 5:   log likelihood = -74.780982  

Random-effects Poisson regression               Number of obs      =
34
Group variable: ship                            Number of groups   =
5

Random effects u_i ~ Gaussian                   Obs per group: min =
6
                                                               avg =
6.8
                                                               max =
7

                                                Wald chi2(4)       =
50.95
Log likelihood  = -74.780982                    Prob > chi2        =
0.0000

------------------------------------------------------------------------
------
    accident |        IRR   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+----------------------------------------------------------
------
    op_75_79 |   1.466677   .1734403     3.24   0.001     1.163259
1.849236
    co_65_69 |   2.032604   .3040933     4.74   0.000     1.516025
2.725205
    co_70_74 |   2.357045   .3998397     5.05   0.000     1.690338
3.286717
    co_75_79 |   1.646935   .3820235     2.15   0.031     1.045278
2.594905
     service | (exposure)
-------------+----------------------------------------------------------
------
    /lnsig2u |  -2.351868   .8586262    -2.74   0.006    -4.034745
-.6689918
-------------+----------------------------------------------------------
------
     sigma_u |   .3085306   .1324562                      .1330045
.7156988
------------------------------------------------------------------------
------
Likelihood-ratio test of sigma_u=0: chibar2(01) =    10.67 Pr>=chibar2 =
0.001

. quadchk

Refitting model intpoints() =  8
factor variables and time-series operators not allowed
in option offset()
error refitting model
r(101);

. 

Best wishes, Garry




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