Re: st: How to get rid of outliers

[Xixi Lin <winnielxx@gmail.com>]

Sergiy,

Thank you so much! You are a life saver. ^_^

Best,
Xixi Lin

On Thu, Oct 24, 2013 at 5:23 PM, Richard Williams
<richardwilliams.ndu@gmail.com> wrote:
> At 03:08 PM 10/24/2013, Xixi Lin wrote:
>>
>> Sergiy,
>>
>> One more question to bother you, I tried the single variable and it
>> works. Then I tried to do it by period. The code seems to be not
>> successful.
>>
>> Here is my code:
>> forvalues i=1/496{
>> foreach x in Return_lead1 Momentum Size Volume MB {
>> qui centile `x' if Period==`i', c(0.5 99.5)
>> local y=r(c_1)
>> local z=r(c_2)
>> keep if inrange(`x',`y',`z')& Period==`i'
>> }
>> }
>
>
> Everything in periods 2 through 496 is going to get dropped after the first
> time through the loop, because they won't meet the requirement that Period
> == 1. Not sure, but this might work:
>
> drop if !inrange(`x',`y',`z')& Period==`i'
>
>
>
>> Do you know what is wrong with my code? Thank you.
>>
>> Best,
>> Xixi Lin
>>
>> On Thu, Oct 24, 2013 at 3:47 PM, Sergiy Radyakin <serjradyakin@gmail.com>
>> wrote:
>> > Xixi,
>> >
>> > statalist FAQ in 3.1 suggests to "Explain what doesn't work".
>> >
>> > The code I posted removes the persons from NLSW88 dataset shipped with
>> > Stata that report very low or very high wages, compared to the other
>> > people in this dataset (2.5% of low earners and 2.5% of high earners).
>> > It also plots the distribution graph, to give you an idea of what it
>> > is going to do (keep only people between the two red lines, remove the
>> > persons in the tails).
>> >
>> > The code is here:
>> > do http://radyakin.org/statalist/2013102401/remove_outliers.do
>> >
>> > The picture is here:
>> > http://radyakin.org/statalist/2013102401/wage_cut.png
>> >
>> > The program drops 112 persons, which is roughly .0498 of the sample.
>> > (you can only drop a _whole_ person, so that is not exactly 0.05).
>> >
>> > Now, what "seems to be not working" mean?
>> >
>> > Best, Sergiy Radyakin
>> >
>> >
>> >
>> > On Thu, Oct 24, 2013 at 2:54 PM, Xixi Lin <winnielxx@gmail.com> wrote:
>> >> Hi Sergiy,
>> >>
>> >> I tried your code, but it seems to be not working.
>> >>
>> >> Best,
>> >> Xixi Lin
>> >>
>> >> On Thu, Oct 24, 2013 at 11:55 AM, Sergiy Radyakin
>> >> <serjradyakin@gmail.com> wrote:
>> >>> Xixi, listen to Nick's advice. But if you still want to drop them,
>> >>> here is how:
>> >>>
>> >>> sysuse nlsw88
>> >>> centile wage, c(2.5 97.5)
>> >>> local l=r(c_1)
>> >>> local r=r(c_2)
>> >>> kdensity wage, xline(`l') xline(`r')
>> >>> keep if inrange(wage, `l', `r')
>> >>>
>> >>> Best, Sergiy Radyakin
>> >>>
>> >>>
>> >>> On Thu, Oct 24, 2013 at 10:45 AM, Nick Cox <njcoxstata@gmail.com>
>> >>> wrote:
>> >>>> If the question is simple
>> >>>>
>> >>>> How to get rid of outliers?
>> >>>>
>> >>>> then there is a good simple long answer
>> >>>>
>> >>>> Don't (usually).
>> >>>>
>> >>>> and a good simple short answer
>> >>>>
>> >>>> Don't.
>> >>>>
>> >>>> There are of course even longer answers in many places. The thread
>> >>>> starting at
>> >>>>
>> >>>> http://www.stata.com/statalist/archive/2007-06/msg00185.html
>> >>>>
>> >>>> throws a variety of lights on outliers and immodesty leads me to
>> >>>> recommend
>> >>>>
>> >>>> http://www.stata.com/statalist/archive/2007-06/msg00239.html
>> >>>>
>> >>>> as particularly long-winded, and respect leads me to nominate Richard
>> >>>> Goldstein's concise remark
>> >>>>
>> >>>> http://www.stata.com/statalist/archive/2007-06/msg00240.html
>> >>>>
>> >>>> as most penetrating of all. But the whole thread is worth looking
>> >>>> through
>> >>>>
>> >>>> One rather long footnote to the thread is provided by
>> >>>>
>> >>>> SJ-13-3 st0313  . . . . . . . . . . . . . .  Speaking Stata: Trimming
>> >>>> to taste
>> >>>>         (help trimmean, trimplot if installed)  . . . . . . . . . .
>> >>>> N. J. Cox
>> >>>>         Q3/13   SJ 13(3):640--666
>> >>>>         tutorial review of trimmed means, emphasizing the scope for
>> >>>>         trimming to varying degrees in describing and exploring data
>> >>>>
>> >>>> but the best Stata incantation of all is likely to be -glm-.
>> >>>>
>> >>>> More generally, modify your model so that outliers are accommodated.
>> >>>>
>> >>>> Don't modify your data because they are awkward to analyse.
>> >>>>
>> >>>> Nick
>> >>>> njcoxstata@gmail.com
>> >>>>
>> >>>>
>> >>>> On 24 October 2013 15:31, Xixi Lin <winnielxx@gmail.com> wrote:
>> >>>>> Hi All,
>> >>>>>
>> >>>>> I know it seems to be a very simple question. But I still wanna ask
>> >>>>> how to keep 99%(95%) of the data? Is it just chop off 2 standard
>> >>>>> deviations? How to code it then?
>> >>>>>
>> >>>>> Thanks a lot.
>> >>>>>
>> >>>>> Best,
>> >>>>> Xixi Lin
>> >>>>> *
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>
>
> -------------------------------------------
> Richard Williams, Notre Dame Dept of Sociology
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