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st: -betafit- and -dirifit- updated on ssc


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: -betafit- and -dirifit- updated on ssc
Date   Thu, 7 Sep 2006 16:15:34 +0100 (BST)

Thanks to Kit Baum -betafit- and -dirifit- have been updated on SSC. To
get the update use -ssc install- or -adoupdate-. Descriptions of both
programs are added at the bottom of this message.

The main change is the addition of the command -dbetafit- to -betafit-
and -ddirifit- to -dirifit-. Both display various types of marginal
effects. In other words they help in making statements like "the
proportion of income spent on food decreases with 3 percentage points
if a persons salery increases by one thousand euros while keeping all
other variables at the mean". -betafit- and -dirifit- show effects in
terms of changes in log odds, which some find less interpretable.

The changes also include some bug fixes, improvements of the help files
and improved labeling of the output. Thanks to Pamala Wiepking and
Silvia Balia for useful comments.

Maarten

--- description of -betafit-:
-betafit- deals with dependent variables that are constrained between
zero and one (primarily proportions) by fitting a beta distribution. It
can use two parameterizations: one in terms of two shape parameters,
and one in terms of a location and a scale parameter. The former
(called the conventional parameterization) corresponds to conventional
representation of the beta distribution in the literature and is
primarily useful in cases without explanatory variables, while the
latter (alternative parameterization) can model how the mean proportion
changes as the explanatory variables change, and is thus particularly
usefull in cases with covariates. -betafit- is written by Nick Cox,
Stephen Jenkins, and Maarten Buis.

--- description of -dirifit-:
-dirifit- deals with multiple dependent variables which are constrained
between zero and one and must add up to one, e.g. proportions of the
budget of cities spent on categories school, police, and other. It does
so by fitting the multivariate version of the beta distribution, which
is called the Dirichlet distribution. -dirifit- knows the same two 
parameterizations as -betafit-. -dirifit- is written by Maarten Buis,
Nick Cox, and Stephen Jenkins.


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


		
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