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


From   Tom <tommedema@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: xtlogit: panel data transformation's recast to double makes model incomputable
Date   Wed, 3 Apr 2013 17:09:38 +0200

"close" is a price, and therefore it is always positive. -sum close,
detail- follows (after dropping some outliers in which I am not
interested):
http://pastebin.com/25gm94i0

Because close is always positive I would like to return to the -ladder
close- issue. It turns out that when I supply -noadjust-, i.e. execute
-ladder close, noadjust- it does return some details:
http://pastebin.com/m8Z4YmKd

-noadjust- is simply the -noadjust-  option of -sktest-, used by
-ladder-. The help file says that this is what it does:

    " noadjust suppresses the empirical adjustment made by Royston
(1991) to the overall chi-squared and its significance level and
presents the unaltered test as described by D'Agostino, Balanger, and
D'Agostino (1990)."

But does anyone have a clue why this adjustment would prevent ladder
from returning anything? Also see the results of -sktest close- versus
-sktest close, noadjust-:
http://pastebin.com/tPUf3xE6

Tom

On Wed, Apr 3, 2013 at 4:54 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> 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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