st: new package ldecomp available on ssc

[Maarten buis <maartenbuis@yahoo.co.uk>]

Thanks to Kit Baum a new package is available on ssc: -ldecomp-.  This
package decomposes the total effects in a logistic regresion into
direct and indirect effects, and is described below and in more detail
in this working paper: http://home.fsw.vu.nl/m.buis/wp/ldecomp.html .
If interested type in Stata -ssc describe ldecomp- and 
-ssc install ldecomp-

-- Maarten

description:
ldecomp decomposes the total effects of a categorical variable in
logistic regresion into direct and indirect effects using a method
by Erikson et al. (2005) and a generalization of this method by
Buis (2008). Consider an example where social class has an indirect
effect on attending college through academic performance in high
school. The indirect effect is obtained by comparing the proportion of
lower class students that attend college with the counterfactual
proportion of lower class students if they had the distribution of
performance of the higher class students. This captures the association
between class and attending college due to differences in performance.
The direct effect of class is obtained by comparing the proportion of
higher class students with the counterfactual proportion of lower class
students if they had the same distribution of performance as the higher
class students. This way the variable performance is kept constant. If
these comparisons are carried out in the form of log odds ratios than
the total effect will equal the sum of the direct and indirect effects.
In its original form this method assumes that the variable through
which the indirect effect occurs is normally distributed. This is
generalized by Buis (2008) by allowing this variable to have any
distribution, which has the added advantage of simplifying the method.

References:
Buis, M.L. (2008). Direct and indirect effects in a logit model. 
http://home.fsw.vu.nl/m.buis/wp/ldecomp.html

Erikson, R, J.H. Goldthorpe, M. Jackson, M. Yaish, D.R. Cox (2005). On
class differentials in educational attainment.  Proceedings of the
National Academy of Science, 102(27): 9730-9732.


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

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

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


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