Re: Mixture model with logistic regression
Hi Mark,
My first suggestion is you can start from simpler mixture model (e.g. 2
distributions) and only focus on those have AEs. 68% patients without AE is
a big disturbance to intercept. Only negative infinity of intercept in
logistic model can give a probability=0. Secondly, you can try to use SAEM
method with mu reference. Based on my own experience, FOCE method is not as
powerful as SAEM in likelihood estimations. Good luck.
BW,
Yucheng Sheng
UCL School of Pharmacy
29-39 Brunswick Square
London WC1N 1AX
Email. [email protected]
Quoted reply history
On 19 February 2016 at 22:30, Mark Sale <[email protected]> wrote:
> Has anyone every tried to use a mixture model with logistic regression? I
> have data on a AE in several hundred patients, measured multiple times
> (10-20 times per patient). Examining the data it is clear that,
> independent of drug concentration, there is very wide distribution of this
> AE, 68% of the patients never have the AE, 25% have it about 20% of the
> time and the rest have it pretty much continuously, regardless of
> drug concentration. (in ordinary logistic regression, just glm in R, there
> is also a nice concentration effect on the AE in addition). Running the
> usual logistic model, not surprisingly, I get a really big ETA on the
> intercept, with 68% of the people having ETA small negative, 25% ETA ~ 1
> and 7% ETA ~ 10. No covariates seem particularly predictive of the post hoc
> ETA. I thought I could use a mixture model, with 3 modes, but it refused
> to do that, giving me essentially 0% in the 2nd and 3rd distribution, still
> with the really large OMEGA for the intercept. Even when I FIX the OMEGA
> to a reasonable number, I still get essentially no one in the 2nd and 3rd
> distribution. I tried fixing the fraction in the 2nd and 3rd distribution
> (and OMEGA), and it still gave me a very small difference in the intercept
> for the 2nd and 3rd populations.
>
> Is there an issue with using mixture models with logistic regression? I'm
> just using FOCE, Laplacian, without interaction, and LIKE.
>
>
>
>
> Any ideas?
>
>
> Mark
>
>
>
> Mark Sale M.D.
>
> Vice President, Modeling and Simulation
>
> Nuventra, Inc. ™
>
> 2525 Meridian Parkway, Suite 280
>
> Research Triangle Park, NC 27713
>
> Office (919)-973-0383
>
> [email protected] http://[email protected]
>
> www.nuventra.com
>
>
>
>