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st: RE: winsorize the effect of outliers (?)


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: winsorize the effect of outliers (?)
Date   Wed, 8 Nov 2006 16:13:59 -0000

Maarten Buis has already drawn attention to relevant 
stuff. But other comments are possible: 

1. Only those who recognise the reference "Cleary (1999)"
can say precisely what he or she did. I guess that -2 
and 2 means winsorize 2 at the bottom and 2 at the top 
but I don't then know what 1 and 0 means. I suspect 
a typo there. 

2. On the evidence here different amounts of winsorizing 
were applied to different variables. If that is 
based on inspection of the data any P-values that follow
are suspect, from at least one point of view. 

3. Winsorizing is a kind of ad hoc method some 50 years
old. Aren't there now better ways of getting model fits
robust to outliers? 

Nick 
n.j.cox@durham.ac.uk 

P.S. I did write -winsorize-, but I never use it. Someone
asked how to do it.... 

dist@interfree.it
 
> In an working paper I read: "To avoid the effect of outliers, 
> we winsorized the observations [time series panel data] 
> following Cleary (1999). The cutoff value are -2 and 2 for 
> "var1[_t-1]", -5 and 5 per "var 2[_t-1]", 1 and 0 for "var3". 
> 
> Note: [_t-1] means a value taken in (t-1).
> 
> Given these three variables (var1, var2 and var3), could 
> somebody tell me how to "winsorize" this way? Thank you. 

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