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RE: st: Using univariate models to provide starting values for multivariate analysis


From   jverkuilen <jverkuilen@gc.cuny.edu>
To   <statalist@hsphsun2.harvard.edu>, <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Using univariate models to provide starting values for multivariate analysis
Date   Mon, 9 Mar 2009 13:44:42 -0400

Katherine Boughey asks::

"Is it valid to use values from univariate analysis for starts in -xtmelogit-?" 

It is absolutely valid to give your own starts, though -xtmelogit- is pretty darn good at picking starting values as it more or less does what you propose by fitting a set of simpler models, which are subsequently refined by simultaneous maximization. 

If you are worried about local optima, you may want to force it to start from multiple locations. 

JV

-----Original Message-----
From: K.Boughey@uea.ac.uk
To: statalist@hsphsun2.harvard.edu
Sent: 3/9/2009 8:46 AM
Subject: st: Using univariate models to provide starting values for      multivariate analysis


Dear Statalisters,

I have a dataset that records bat abundance(converted for this analysis to
presence/absence) along 30km transects. Each transect is surveyed twice a
year giving two levels of clustering: surveys nested in transects and
transects nested within year.

I hope to model the relationship between bat presence and a variety of
explanatory predictors using -xtmelogit-. I have developed a set of
candidate models each containing a different combination of explanatory
predictors.

In a previous analysis I fitted univariate models for each explanatory
predictor. Is it valid to use these estimates as a starting value for that
predictor in each candidate model in which that predictor appears?

Thanks,

Katherine Boughey

--
Centre for Ecology, Evolution and Conservation
School of Environmental Sciences
University of East Anglia
Norwich
NR4 7TJ


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