Re: st: Standard normal Depvar

[Nick Cox <n.j.cox@stata.com>]

Exponentiation will get you all positives. After that many options are 
open.

Evans Jadotte wrote:

> Nick Cox wrote:
> > This produces zero or positive values.
> >
> > Less pedantically, if the variable is already standard normal, why 
> > does it need transforming?
> >
> > Nick
> >
> > Maarten buis wrote:
> >
> > > --- On Wed, 5/8/09, Evans Jadotte wrote:
> > > > I am trying to run a regression where the dependent
> > > > variable has a standard normal distribution (those of you
> > > > familiar with the "wealth index based on the PCA analysis",
> > > > this is my Depvar).  However, I need to have the prediction  to be 
> > > > all positive to use for transforming.
> > > > How can I transform  the Depvar in order  to
> > > > force  xb^ to take on positive values?
> > >
> > > Here is one option:
> > >
> > > reg y x1 x2
> > > predict yhat
> > > sum yhat, meanonly
> > > gen yhatprime = yhat + abs(r(min))
> >
> > *
> > *   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/
> Thanks to Maarten and Nick for their insight and comment on my question.
>
> I have both negative values and zeros in the /depvar /(/y/)/, /so/ /the 
> forecast, xb,  will reflect such values. And as I will need  sqrt(xb) 
> for further transformation at later stages, I need to transform /y/ so 
> that xb takes on all 'strictly' positive values and still preserve 
> normality of /y/. Maarten's suggestion indeed generates a 0 and the 
> transformation I need is in y (not yhat = xb). I have been trying a 
> Box-Cox power transform but results are not satisfactory.

*
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