The econometricians use the hurdle model, and an analysis that may
complement an analysis of the "hurdle" model is a
TOBIT regression, (this can be set up in SPLUS or LIMDEP
http://www.biostat.wustl.edu/archives/html/s-news/2000-03/msg00213.html)
or a "Two Part Model" (
Duan N, Manning WG Jr, Morris CN, Newhouse JP. Choosing between the
sample selection model and the multi-part model. Journal
of Business and Economic Statistics. 1984 July; 2(3):283-289.
Duan N. Smearing estimate: A nonparametric retransformation method. J.
of the American Statistical Assc. 1983 Sept; 78:605-610.
Duan N, Manning WG Jr, Morris CN, Newhouse JP. A comparison of
alternative models for the demand for medical care. Journal of
Business and Economic Statistics. 1983 Apr; 1(2):115-126.)
I recall the HMISC() library has a smearing function.
--
Chris Barker
Biostatistics
Genentech, Inc., M/S 66
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www.gene.com
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FAX: 650 - 225 - 4538
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