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Re: st: ladder question for right-skewed variable


From   David Hoaglin <dchoaglin@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: ladder question for right-skewed variable
Date   Thu, 25 Apr 2013 20:44:58 -0400

Gabriel,

The ratio of the largest value to the smallest value is quite large,
so a transformation is likely to be useful.  As a first step ("first
aid"), I suggest that you try the logarithm (base 10).

Usually the context of the data plays a role in the choice of a
transformation, so that the result is meaningful.  What is the nature
of disp_2000?

With 1010 observations you should check whether the data has some
structure (e.g., two or more modes or groups), for example, by making
a histogram with a sizable number of bins (say 25 or so).  If you find
structure, you will need to deal with that also.

David Hoaglin

On Thu, Apr 25, 2013 at 8:11 PM, Gabriel Nelson
<lgabrielnelson@gmail.com> wrote:
> I have a variable that is right-skewed.  I used the the ladder command
> to see suggested transformations. However, no transformations appeared
> in the output. I'm guessing that this does not mean the raw form is
> better, because there is an option for 'raw' on this list.
>
> Here is the output for the sum, detail command for the variable:
>
>
>
> sum disp_2000, detail
>
>       Number displaced 2000 (if data unavailable go up
>                            to 2003
> -------------------------------------------------------------
>
>       Percentiles      Smallest
>  1%            1              1
>  5%            2              1
> 10%            3              1       Obs                1010
> 25%            6              1       Sum of Wgt.        1010
>
>
> 50%         15.5                      Mean           281.5297
>                         Largest       Std. Dev.      1217.168
> 75%           82           9421
> 90%        436.5           9505       Variance        1481497
>
> 95%         1251          16255       Skewness       9.012044
> 99%         5953          19569       Kurtosis       108.8061
>
> Any suggestions are greatly appreciated.
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