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Re: st: Using ksmirnov


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Using ksmirnov
Date   Wed, 5 Sep 2012 21:25:20 +0100

Also -qplot- (SJ).

My San Diego talk may be of interest.
http://stata.com/meeting/sandiego12/abstracts/

Nick

On Wed, Sep 5, 2012 at 5:09 PM, Morrison Hodges <hodge002@umn.edu> wrote:

> Nick and Maarten, thank you. My second example does work, when I pick a variable that has data (I haven't any patients in Group 3 yet). Testing Groups 1 and 2 worked as advertised. My bad, as usual. I've downloaded -stripplot- and will look it over.
> Morry
>
> On Sep 5, 2012, at 10:14 AM, Maarten Buis <maartenlbuis@gmail.com> wrote:
>
>> On Wed, Sep 5, 2012 at 4:41 PM, Morrison Hodges wrote:
>>> I'm trying to use ksmirnov to compare 2 distributions to determine if there are any differences in the distribution of the variables.
>>>
>>> I have a .dta file with 179 patients. Each patient is classified as being in one of 7 groups from 1 to 7, i.e., group==1, group==2, etc. I want to compare the same variable between 2 groups. All variables are already sorted, from lowest to highest.
>>
>> For such a small sample size like that I would use Nick Cox's
>> -stripplot- (see: -ssc desc stripplot-). The power of tests like
>> -ksmirnov- is usually pretty bad, so in small sample sizes you are not
>> going to find anything that is not glaringly obvious if you just
>> looked at the data. On the other hand you will in all likelihood miss
>> lots of real an interesting patterns if you focus on such low power
>> tests. So, there is no added value to be got from these tests and a
>> real chance of a loss.
>>
>> -- Maarten
>>
>> ---------------------------------
>> Maarten L. Buis
>> WZB
>> Reichpietschufer 50
>> 10785 Berlin
>> Germany
>>
>> http://www.maartenbuis.nl
>> ---------------------------------
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