Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: How low can the percentage of uncensored cases be in heckprob?


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: How low can the percentage of uncensored cases be in heckprob?
Date   Tue, 11 Nov 2008 17:15:03 +0000 (GMT)

--- "Tyler, Margaret C D" <margaret-tyler@uiowa.edu> wrote:
> In the example in the Stata reference -H heckprob, there are 95 total
> and 59 uncensored observations, so 62% are uncensored. In my own
> situation I have only about 19% uncensored. Is it still appropriate
> to use heckprob for my analysis? I have run the equations and gotten
> what seem to be valid results. rho is non-significant.

You are obviously pushing your luck with that many censored cases. It
is no longer very popular to make statements like you need at least N
observation or p% uncensored cases for technique t to be appropriate
(whatever appropriate may mean). So I don't think you will get the
answer you are looking for. However, what you can do is run some
simulations and see how well (or bad) your estimator behaves with a
small number of uncensored cases. At the last Summer North American
Stata Users' Group meeting I gave a talk on using Stata for doing this
type of simulations, you can get the materials from: 
http://ideas.repec.org/p/boc/nsug08/14.html

Hope this helps,
Maarten


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

visiting address:
Buitenveldertselaan 3 (Metropolitan), room N515

+31 20 5986715

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


      
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index