Re: st: Re: adjusted percentages and adjusted odds ratios

[Michel Camus <mcamus@videotron.ca>]

May I suggest that you submit a bit more info to the list?
Can you say something about the model used to estimate the adjusted OR 
and the method used to adjust the percentages?
What variables were used, what main effect was estimated?
Are the adjusted percentages obtained from a different model or are they 
computed from results of  "-predict" ?

A few things seem odd. The gap between the calculated OR (1.17) from the 
adjusted percentages and the adjusted OR (1.7) seems inexplicable, 
unless ...
   1) the covariates modelled were not the same,
   2) the samples used for the predictions are not the same 
(e.g.e(sample) used or not in predicting),
   3) the effect measured is not the same (e.g. one case specifies "due 
to cost" and the other "for any reason"),
or 4) an interaction term is entered in one model, not in the other.

I don't understand the study design. How did you select your subjects?
Could you select patient who cut back medication vs. patients who did 
not cut back, OR who cut back for other reasons, and then considered 
their type of insurance? This approach would seem unlikely to me.
If instead you selected and compared VA vs. private insurance holders as 
to whether or not and why they cut back their meditation, then should 
you not be computing the RR instead of the OR?

Michel

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Michel Camus, Ph.D.

Epidemiologist, Biostatistics and Epidemiology Div., HECSB, Health Canada

Courriel / e-mail : mcamus@videotron.ca <mailto:mcamus@videotron.ca>

Téléphone / phone     :    (514) 850-0157

Télécopieur / fax        :    (514) 850-0836

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> > -----Original Message-----
> > From: Copeland, Laurel
> > Sent: Friday, September 19, 2003 11:26 AM
> > To: Eby, Elizabeth
> > Cc: VHAANN HSRD Statistical Group
> > Subject: RE: adjusted percentages
> >
> >
> > The raw odds ratio can be calculated...17% of 334=277, 20% of 2741=2193
> > cut back?
> >    no  yes
> > priv no   277  57
> > ins? yes 2193 548
> >
> > OR = (277/57) / (2193/548)
> >   =  4.86  /  4.00
> >   = approx 1.22
> > The remainder of the effect in the adjusted OR must be due to the
> > covariates.
> >
> > -----Original Message-----
> > From: Eby, Elizabeth
> > Sent: Friday, September 19, 2003 11:05 AM
> > To: VHAANN HSRD Statistical Group
> > Subject: adjusted percentages
> >
> > How would you explain the small difference in the adjusted percentages
> >    
> (17%
>  
>
> > vs 20%) with an odds ratio of 1.7 (p=.04)?  Does it have anything to do
> >    
> with
>  
>
> > the underlying sample sizes of the 2 groups (n=334 VA patients and n=2741
> > with private insurance)?
> >
> > Thanks.
> >
> > -----Original Message-----
> > From: jpiette@umich.edu [mailto:jpiette@umich.edu]
> > Sent: Friday, September 19, 2003 10:51 AM
> > To: elizabeth.eby@med.va.gov
> > Subject:
> >
> > Liz - can you double check this?  THe difference in %'s seem small
> >    
> relative
>  
>
> > to
> > the AOR.
> >
> > Controlling for their sociodemographic characteristics, number of chronic
> > diseases, and number of prescription medications, 17% of VA patients cut
> > back
> > on medication use due to cost compared to 20 % of those with private
> > insurance
> > (adjusted odds ratio [AOR]: 1.7, p=.04),
> > *
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