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From |
Nick Cox <njcoxstata@gmail.com> |

To |
"statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |

Subject |
Re: st: ladder question for right-skewed variable |

Date |
Fri, 26 Apr 2013 19:20:19 +0100 |

Just to underline that kurtosis in your variable was calculated by -summarize- 108. That's BIG. No wonder -sktest- can't cope. Nick njcoxstata@gmail.com On 26 April 2013 19:17, Nick Cox <njcoxstata@gmail.com> wrote: > That's not quite "no transformations appeared in the output" as > -ladder- is signalling P-values for some cases. > > But I readily agree that -ladder- is not doing a good job here at all. > > In fact, I am now reminded of evident -ladder- problems shown in a > recent thread starting at > http://www.stata.com/statalist/archive/2013-02/msg00862.html > > I can't find a public email, even though I thought I posted on this, > but my impression from looking at the code is that -ladder- is > essentially fragile. The real problem here is within -sktest-. It can > break down, it seems, for large sample sizes and/or large deviations > from Gaussianity. Then it bounces back missings. > > I think you just need to abandon -ladder-. It's not essential. You > don't need _any_ test to tell you that some transformation will help > if the goal is to reduce asymmetry, and there are only a few credible > alternatives. > > As David and I pointed out, log transformation should work quite well > for your data, > > but but but: (my suggestion; David may not agree) why transform at > all? Your solutions start with -poisson- (or, for consenting adults, > -nbreg-). > > BTW, -ladder- is a command, not a function, and in Stata ne'er the > twain shall meet. > > Nick > njcoxstata@gmail.com > > > On 26 April 2013 18:55, Gabriel Nelson <lgabrielnelson@gmail.com> wrote: >> Thanks Nick, yes exactly, my question is why the ladder function fails >> to provide any chi-square values here. I'll attach the Stata output >> here: >> >> . ladder disp_2000 >> >> Transformation formula chi2(2) P(chi2) >> ------------------------------------------------------------------ >> cubic dis~2000^3 . . >> square dis~2000^2 . . >> identity dis~2000 . . >> square root sqrt(dis~2000) . 0.000 >> log log(dis~2000) . 0.000 >> 1/(square root) 1/sqrt(dis~2000) . 0.000 >> inverse 1/dis~2000 . 0.000 >> 1/square 1/(dis~2000^2) . 0.000 >> 1/cubic 1/(dis~2000^3) . 0.000 >> >> . 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 >> >> On Fri, Apr 26, 2013 at 10:47 AM, Nick Cox <njcoxstata@gmail.com> wrote: >>> Please see my answers too. You have still not given the exact -ladder- >>> command you used or its output, so it is really difficult to know what >>> is going on. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: ladder question for right-skewed variable***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: ladder question for right-skewed variable***From:*Gabriel Nelson <lgabrielnelson@gmail.com>

**Re: st: ladder question for right-skewed variable***From:*David Hoaglin <dchoaglin@gmail.com>

**Re: st: ladder question for right-skewed variable***From:*Gabriel Nelson <lgabrielnelson@gmail.com>

**Re: st: ladder question for right-skewed variable***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: ladder question for right-skewed variable***From:*Gabriel Nelson <lgabrielnelson@gmail.com>

**Re: st: ladder question for right-skewed variable***From:*Nick Cox <njcoxstata@gmail.com>

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