Some more thoughts:
As we have been reminded by Alan Reese & Nick Cox
Stata consistently treats missing as true.
By contrast, all given SPSS's logical expressions are
correct if "missing" is read as "false". Moreover, in their own words:"The
assignment is executed only if the logical expression is true."
However, I am not sure how SPSS evaluates "not missing".
I would expect SPSS to treat it as "missing".
If we are to change this, I would like two things:
A warning when missing values are evaluated in a logical expression
An option to reset the logical value of "missing" to either true (default),
false, or error. If error is selected, evaluating logical expressions
including missing values will generate an error code, and (usually)
stop execution of code.
If available, I would probably set missing = error in most programs,
as it is is almost always a mistake when I do not error-trap the
missing values.
Whatever else StataCorp decide to do, I would expect the current
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