Re: st: My last word on strange world

[Richard Williams <Richard.A.Williams.5@ND.edu>]

At 11:35 AM 1/11/2008, William Gould, StataCorp LP wrote:
> It therefore follows
>
>      x>=100      evaluates to false if x is missing
>
> and thus the statements (x>=100) and (x<100) are both false and, as I asked
> about Jeph's comment, is that really in line with the expectations of
> ordinary users?
It is with mine.  To me, missing is not a number, large or 
small.  And, because of that, in practice the coding is usually more like

x > = 100 & !missing(x)

which I find awkward and mistake prone.  My own preference would 
therefore be that the statements be more like

x>=100
x<100
missing(x)

One and only one of the above three would be true.  This also makes 
it explicit that how to handle missing is a separate decision.

There are going to be gotchas with any system.  I therefore think 
that the default should be whatever people are likely to want most 
frequently.  And I think it is relatively rare that when you have a 
statement like

x>=100

that people intend for missing to be evaluated as true.  If they do, 
that is when they can go to the extra work and code

x>=100 | missing(x)


-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
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