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Re: st: RE: ml and parmby versus statsby

From   "Roger B. Newson" <>
Subject   Re: st: RE: ml and parmby versus statsby
Date   Wed, 12 Dec 2012 16:10:16 +0000

I don't know how your -statsby- and -parmby- results are different, as you haven't told us. However, -statsby- creates a dataset with 1 observation per by-group, and different variables for the estimates and standard errors for different parameters. -parmby-, on the other hand, creates a dataset with 1 observation per parameter per by-group, with 1 variable for the estimate and 1 variable for the standard error, and other variables for the confidence limits and P-values.

I am a bit mystified about the -quietly- option for -parmby-. As the author of -parmby-, I never knew that -parmby- had a -quietly- option, although it can take the -quietly- prefix like other Stata commands.

I hope this helps.

Best wishes


Roger B Newson BSc MSc DPhil
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton Campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Web page:
Departmental Web page:

Opinions expressed are those of the author, not of the institution.

On 12/12/2012 15:52, S. Suetens wrote:

Is there anyone who can explain why maximum likelihood estimation gives different results under parmby as compared to statsby?
I have run the two commands below (based on the same likelihood function) and they give very different parameter estimates and standard errors.

statsby _b _se, by(id) saving("D:\Statsby.dta", replace) nodots: ml model lf MaxLik (lambda: strategy =) (rhosigma: RHO SIGMA, nocons), max difficult

parmby "ml model lf MaxLik (lambda: strategy =) (rhosigma: RHO SIGMA, nocons), max difficult", by(id) saving("D:\Parmby.dta", replace) quietly

Thanks in advance for any help.

Sigrid Suetens
Associate Professor
Department of Economics
Tilburg University

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