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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 15:57:17 +0100

The first is quite wrong because _only_ a single variable name can be
given as the argument to -by()-.

The second looks exactly right to me, so I don't understand why you
got an error message (presumably what you meant).

. sysuse auto
(1978 Automobile Data)

. ksmirnov mpg if rep78 == 4 | rep78 == 5, by(rep78)

Two-sample Kolmogorov-Smirnov test for equality of distribution functions

 Smaller group       D       P-value  Corrected
 ----------------------------------------------
 4:                  0.4899    0.038
 5:                 -0.0303    0.988
 Combined K-S:       0.4899    0.075      0.041

Note: ties exist in combined dataset;
      there are 16 unique values out of 29 observations.

(I still think Kolmogorov-Smirnov usually a waste of time.)

Nick

On Wed, Sep 5, 2012 at 3:41 PM, Morrison Hodges <hodge002@umn.edu> 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.
>
> 'ksmirnov' requires by(groupvar). I tried:
>
> ksmirnov var, by(group==1, group==3)
>
> and I get an error message that says "invalid variable in by() option.
>
> I tried: ksmirnov jumps if group==1 | group==3, by(group)
> and also got an error method. Can someone help? Thanks, Morry Hodges
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