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Re: st: sktest


From   Ronan Conroy <rconroy@rcsi.ie>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: sktest
Date   Fri, 23 Aug 2002 10:23:27 +0100

on 22/8/02 10:15 PM, Michael Cha at mikecha0@lycos.com wrote:

> Would you please let me know how to interpret them?
> In addition, is there any other useful command to test skewness, kurtosis and
> normality, please let me know.

Graphs are your first option. Numeric indices tend to tell you little. Try
-qnorm- and -pnorm-. Look out for
A) smooth curves - usually a sign that a re-expression may help in the
analysis
B) graininess - the plot goes up in a series of steps, indicating that the
variable takes on a restricted range of values, such as integers only. In
the case of very grainy data, you may have to consider models for count data
or for ordered categorical variables.
C) tails that twist abruptly. Not a healthy sign - the data may be censored
(the measuring instrument may not be able to measure values outside a
certain range). 


Ronan M Conroy (rconroy@rcsi.ie)
Lecturer in Biostatistics
Royal College of Surgeons
Dublin 2, Ireland
+353 1 402 2431 (fax 2329)

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