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Re: st: xtlogit: panel data transformation's recast to double makes model incomputable


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: xtlogit: panel data transformation's recast to double makes model incomputable
Date   Wed, 3 Apr 2013 15:54:59 +0100

The transformations that -ladder- tries are typically only defined for
positive variables. As I recall, many of your variables are variously
positive and negative.

The usual transformations for right-skewed variables, such as square
root and logarithmic, are thus no use in your case.

This is precisely why cube root and inverse hyperbolic functions were
suggested earlier/

On the face of it that is not an explanation of why all the
transformations fail, but I'd not be inclined to think that -ladder-
will help your problem.

I'm afraid that you have keep reminding us of basics -- e.g. what is
-close- and what are its descriptive statistics -- as even those
following your threads can't be expected to keep track of all earlier
posts.

Nick

On 3 April 2013 15:33, Tom <tommedema@gmail.com> wrote:

> Anyway, I think I may have a very important pointer that could help in
> finding the cause of this issue:
> when I run -ladder close- it returns absolutely nothing, i.e.:
>
>  ladder close
>
> Transformation         formula               chi2(2)       P(chi2)
> ------------------------------------------------------------------
> cubic                  close^3                    .            .
> square                 close^2                    .            .
> identity               close                      .            .
> square root            sqrt(close)                .            .
> log                    log(close)                 .            .
> 1/(square root)        1/sqrt(close)              .            .
> inverse                1/close                    .            .
> 1/square               1/(close^2)                .            .
> 1/cubic                1/(close^3)                .            .
>
> I believe this is very much related to the problems I am having with
> this variable, close. If I can determine why ladder refuses to give me
> any transformations, then I may be able to figure out what is the
> source of this issue.
>
> I am not just trying to get an answer, I am interested in why ladder
> is not returning any transformations because this may give me
> information on the root cause of the problem.
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