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Re: st: My last word on strange world


From   "Svend Juul" <[email protected]>
To   <[email protected]>
Subject   Re: st: My last word on strange world
Date   Fri, 11 Jan 2008 12:40:43 +0100

So many trying to get the last word on a problem that won't go away.

I read Bill Gould's comments as a bit softer than they used to be, but I
may be mistaken. Bill writes: "... the problem of missing values and the
number line are inherent"

Yes, but does that make it necessary to 
   - let (x) evaluate to true if x is missing:
      . gen y=1 if x
   - let (x>100) evaluate to true if x is missing:
      . gen y=1 if x>100

Obviously, some decision was needed. The decision made is perfectly
logical, but the following alternative is equally logical and much more
in line with the expectations of ordinary users: 
   - let (x) evaluate to false if x is missing
   - let (x>100) evaluate to false if x is missing
   - let (x==100) evaluate to false if x is missing
   - let (x<100) evaluate to false if x is missing
   - let (x==.) evaluate to true if x is . (missing)

Nick Cox asks: "What do you consider appropriate Stata behaviour for 
   . list x if x > 42 
   . regress z y if x > 42"
This is easy: I consider it appropriate to omit observations with x
missing in both situations.

I do not care about the internal value of missings (this is why I bought
a statistical package program), and I see no problem in the way -sort-
handles them.

Bill Gould: "The observations containing missing values need to be easy
to identify and classify". Don't the missing() function and egen's
rowmiss() and rownonmiss() do that perfectly?

Last word? Hardly.

Svend

__________________________________________

Svend Juul
Institut for Folkesundhed, Afdeling for Epidemiologi
(Institute of Public Health, Department of Epidemiology)
Vennelyst Boulevard 6
DK-8000  Aarhus C, Denmark
Phone:   +45 8942 6090
Mobile:  +45 2634 7796
Email:   [email protected]
__________________________________________ 

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