Tuesday, July 31, 2007

Mplus vs. aML

I am working on a joint model of miscarriage and child mortality. The idea is that higher rate of miscarriage may end up with a more highly selected newborns, who are less vulnerable to premture death. This is a Heckman selection type of model, with the exception that the main equation is a hazard model instead of a continuous model. I have been trying to make Mplus to do the job, as hinted by Bengt (http://www.statmodel.com/discussion/messages/11/740.html?1155563326). Then I got a direct response from Linda that this type of model cannot be estimated using Mplus (http://www.statmodel.com/discussion/messages/14/2459.html?1185842830). I guess this leaves me no other alternatives but to go to aML.

aML is a fine software. I used it in 2004 for a chapter of my dissertation (at that time it cost about 1,000 bucks). Now it is free and open-source, and everyone can look at the code (in FORTRAN) to see how certain things are done. I am a little surprised that it has not attracted more attention.

What I would really like to see is a wrapper program in Stata and can 1) export data to aML, 2) automatically generate sensible starting values and feed them to aML, and 3) gather coefficients estimated in aML for post-estimation manipulation.

If nobody has already started working on this, I might end up doing it myself.

Friday, July 27, 2007

LyX 1.50 is out, with unicode support

LyX 1.50 seems to be a real alternative to MS Office and OpenOffice for serious writing. Now it has unicode support built in. I have tried it on both Windows and Linux and it works jus fine. What I have not figured out is how to get the file compiled with LaTeX into DVI file correctly when there are double-byte characters (Chinese, for example).