Hi Doran, 

My interests to estimate fixed effects parameters in a mixed model (not the 
random effects parameters) and, in addition, in the model there are some 
nuisace parameters. For this estimation I am using pseudo-maximum likelihood 
methods. First I am estimating nuisance parameters then using these estimates 
in my likelihood function to get the estimates of fixed effects parameters 
using lmer2. Therefore, to get the correct estimates of the standard errors, I 
need robust (or sandwich) estiamtes of the SE. Thank you and thanks to Thomas 
his remarks, 

Sattar


----- Original Message ----
From: Thomas Lumley <[EMAIL PROTECTED]>
To: "Doran, Harold" <[EMAIL PROTECTED]>
Cc: Sundar Dorai-Raj <[EMAIL PROTECTED]>; Abdus Sattar <[EMAIL PROTECTED]>; 
[EMAIL PROTECTED]; [EMAIL PROTECTED]
Sent: Wednesday, September 19, 2007 1:13:20 PM
Subject: Re: [R] Robust or Sandwich estimates in lmer2


On Wed, 19 Sep 2007, Doran, Harold wrote:

> This has come up before and I'll again ask the question "why would you
> want robust standard errors in lmer"?

And I'll again answer: using lmer() does not automatically guarantee correct 
model specification, either for the correlation structure or for the marginal 
variance.

      -thomas


Thomas Lumley            Assoc. Professor, Biostatistics
[EMAIL PROTECTED]    University of Washington, Seattle


      
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