[R-sig-ME] within-group averaging

Jarrod Hadfield j.hadfield at ed.ac.uk
Thu Nov 29 11:13:57 CET 2012

Hi David,

Thank you for the email. I hadn't come across the term coarsening  
before, but I see from the paper that you sent that what I described  
is nonignorable coarsening. Now to try and deal with it, without  
(hopefully) having to augment with the true values of x.



Quoting David Duffy <David.Duffy at qimr.edu.au> on Thu, 29 Nov 2012  
20:01:39 +1000:

> On Thu, 29 Nov 2012, Jarrod Hadfield wrote:
>> Hi Jonas,
>> Thanks for your reply. Initially, I thought it was solely to do  
>> with inhomogeneity too, and I agree that it plays a role. However,  
>> if you replace
>> cuty<-cut(y,10) with cuty<-cut(x,10) (i.e. define groups by bins of  
>> x rather than y) then the problems with bias and type-I error rate  
>> disappear despite the same pattern of inhomogeneity existing.
> If you plot your xbar2_cuty v. xbar and xbar2_cutx v. xbar you will  
> see the latter is symmetrical around the line of identity, while the  
> former is biased in the direction of the y~x regression line. The  
> nonrandom coarsening of a subset apparently can affect inference
> (A quick google obtained  
> http://biostatistics.oxfordjournals.org/content/8/4/722.full)
> | David Duffy (MBBS PhD)                                         ,-_|\
> | email: davidD at qimr.edu.au  ph: INT+61+7+3362-0217 fax: -0101  /     *
> | Epidemiology Unit, Queensland Institute of Medical Research   \_,-._/
> | 300 Herston Rd, Brisbane, Queensland 4029, Australia  GPG 4D0B994A v

The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.

More information about the R-sig-mixed-models mailing list