Re: st: ZOIB procedure

[Prerna S <maruiprerna@gmail.com>]

Hello Cam,

Tobit would be inappropriate for the data I am using because the data
are not censored, rather they are defined over [0,1]. From a quick
glance, it appears that arcsine is appropriate for binomial data,
which again my data are not. However, I am unfamilar with arcsine and
gllamm so I'll look over the references provided. Thank you.

Prerna



On 18 September 2011 20:02, Cameron McIntosh <cnm100@hotmail.com> wrote:
> Hi Prerna,
>
> I have been wondering about simultaneous equation models (SEMs) that integrate Beta regression links, but I don't think anyone has done the computer implementation on this yet. That would solve your problem a bit more elegantly than SUR approaches as you could easily allow corr(e1,e2). That would certainly be a good R project. :)
>
> Anyway, you may want to just switch to a logit or tobit model. Natural scientists (especially in biology and ecology) have long favoured arcsine(square root) transformations for dealing with proportions but this has been criticized recently by:
> Warton, D.I., & Hui, F.K.C. (2011). The arcsine is asinine: the analysis of proportions in ecology. Ecology, 92(1), 3–10. http://www.esajournals.org/doi/pdf/10.1890/10-0340.1
>
> who recommend logistic regression for analyzing proportions. You could estimate an SEM with logit links in gllamm, allow corr(e1,e2) and also instrument X if it's endogenous and if you have some defensible instruments in your data set.
> My two cents,
>
> Cam
>
>> From: maruiprerna@gmail.com
>> Date: Sun, 18 Sep 2011 17:51:07 -0400
>> Subject: st: ZOIB procedure
>> To: statalist@hsphsun2.harvard.edu
>>
>> Dear Statalisters,
>>
>> I am using zoib (Stata 11.2) to estimate 2 proportions. I have 3 questions.
>>
>> 1. The model that I am attempting to estimate looks like the following.
>>
>> p1 = a1 + a2X + e1
>> p2 = b1 + b2X + e2
>>
>> where pi is the proportion of income from source i.
>>
>> Is there any procedure that approximates an SUR for zoib that I can
>> use? I tried the suest option but it does not offer a test statistic
>> and the results under suest appear to be the same as without suest. I
>> am unsure if this implies that SUR does not matter or if I missed
>> something.
>>
>> 2.  Wooldridge (2002) suggests using Smith-Blundell/Rivers Vuong
>> method that for dealing with endogeneity with respect to fractional
>> logit and tobit. Is this for some reason unsuitable for zoib?
>>
>> 3.  I would like to investigate the usual problems like
>> multicollinearity, heteroscedasticity, non-normality. Is there a
>> resource that I might refer to for regression diagnostics for zoib?
>>
>>
>> Thank you for you time.
>>
>> Prerna Marui
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