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RE: Missing values [was: RE: st: simple question]

From   "Nick Cox" <[email protected]>
To   <[email protected]>
Subject   RE: Missing values [was: RE: st: simple question]
Date   Wed, 2 Jun 2004 23:07:58 +0100

Richard Williams
> Sure.  What I dislike is that, unlike other programs, Stata 
> forces you to 
> recode the MD values from a data set.  All those 7s, 9s, 99s, 
> etc. will 
> have to be recoded to .a, .b, etc.  The values you use for MD 
> will not be 
> the same as the values in the published codebooks or that may 
> be reported 
> by other users of the data who are using other programs.
> In SPSS, on the other hand, I would just say something like
> Missing Values X (77, 88, 99).
> This isn't a mega problem, but when Stata expanded its 
> possible MD codes 
> I'd have rather seen it take an SPSS-type approach than the 
> route it did 
> go.  (On the other hand, I suppose you could argue that the 
> rest of the 
> world should do things more like Stata.)

I just wonder what that means internally when SPSS does 
calculations. Perhaps it can be done more efficiently 
than would be guessed at first sight. Perhaps SPSS creates 
a copy of X with which it does all the work and hides 
that from the user. In contrast Stata appears much more 
upfront with the user about what is happening. As has often 
been said, Stata makes the assumption that the user is 
a smart person. 

> The bigger problem (which is perhaps more of an issue with 
> Stat/Transfer 
> than it is with Stata) is that distinctions between types of 
> MD codes get 
> lost when converting from SPSS to Stata. I don't know whether 
> this problem 
> is unique to Stata or occurs with other types of conversions 
> as well, but I 
> would like to see software better address it, e.g. when there 
> are multiple 
> MD codes in SPSS assign them to .a, .b, etc. in Stata.

Clearly an issue for Stat/Transfer to discuss. 

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