I just noticed Martin Buis's new -seqlogit- command which looks very
interesting. How does it improve on Rory Wolfe's -ocratio- command? An
obvious improvement is the Stata version, 9.2 versus 5.0. Are there
other improvements? Unfortunately, I cannot attend the user meeting on
September 7.
Anders Alexandersson
andersalex@gmail
On 8/16/07, Maarten buis <[email protected]> wrote:
> Thanks to Kit Baum a new package called -seqlogit- is now available on
> ssc. This package fits a sequential logit model. Traditionally, the aim
> of a sequential logit model is to study a process that can be described
> as a series of choices between a small number of options. However,
> these choices eventually lead to an end result. The aim of this package
> is to not only study the effects of explanatory variables on these
> choices (study the process), but also study the effects on the end
> result.
>
> For example, in education parents make a series of choices at what type
> of schools to send their children. Typically, the aim of the model is
> explore the effects of explanatory variables on the probabilities of
> continuing from one level to the next, i.e. study the process through
> which education is attained. However, in the end this process lead to
> an outcome: highest achieved level of education. Both the process and
> the end result are of substantive interest and are related to one
> another, but they are not the same.
>
> This package implements a method by Buis (2007) to study simultaneously
> the effect of explanatory variables on the process (the probability of
> passing from one level to the next) and the final outcome (highest
> achieved level). The effect of the explanatory variable on the end
> result can be shown to be a weighted sum of the log odds of passing the
> transitions. The weights are the product of the following three
> elements:
>
> o the proportion of people at risk of passing the transition, so a
> transition receives more weight if more people are at risk of passing
> it.
> o the variance of the dummy indicating whether the transition was
> passed or not, so a transition receives more weight if close to 50%
> pass, and less weight if virtually everybody passes or fails that
> transition.
> o the expected difference in outcome between those that pass and those
> that fail the transition, so a transition receives more weight if
> people gain more from passing it.
>
> -seqlogit- will estimate a sequential logit and allows one to use
> -predict- to predict the weights, and its components. Furthermore, it
> contains the -seqlogitdecomp- command, which graphically displays the
> decomposition of the effect of the explanatory variable on the end
> result into the effects of the explanatory variable on the individual
> transitions and their weights.
>
> This package also contains three ancillary files, that describe an
> example. The files are a do-file that implements the example, the
> dataset used by the do-file, and a pdf-file which shows the output and
> explains some of the tricks used in the example. To install the package
> and the ancillary files type -ssc install seqlogit, all-
>
> I will give a presentation on this package on Friday September 7 at the
> 2007 Nordic and Baltic Stata Users Group meeting.
>
>
> Note:
> What I call here a sequential logit model is also known under a number
> of different names: sequential response model (maddala 1983),
> continuation ratio logit (Agresti 2002), model for nested dichotomies
> (fox 1997), and the Mare model (shavit and blossfeld93) (after (Mare
> 1981)).
>
>
> References:
>
> Agresti, Alan 2002 . Categorical Data Analysis, 2nd edition. Hoboken,
> NJ: Wiley-Interscience.
>
> Buis, Maarten L. 2007 ``Not all transitions are equal: The relationship
> between inequality of educational opportunities and inequality of
> educational outcomes'' http://home.fsw.vu.nl/m.buis/wp/distmare.html.
>
> Fox, John 1997 Applied Regression Analysis, Linear Models, and Related
> Methods. Thousand Oaks: Sage.
>
> Maddala, G.S. 1983 Limited Dependent and Qualitative Variables in
> Econometrics Cambridge: Cambridge University Press.
>
> Mare, Robert D. 1981 ``Change and Stability in educational
> stratification'' American Sociological Review, 46(1), p.p. 72-87.
>
> Shavit, Yossi and Hans-Peter Blossfeld 1993 Persistent Inequality:
> Changing Educational Attainment in Thirteen Countries Boulder: Westview
> Press.
>
>
>
> -----------------------------------------
> 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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