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Re: st: Re: NaN (the inedible kind)
At 08:18 26/09/02 -0400, Kit Baum wrote:
IMHO Stata does NOT make use of NaNs, which have the properties that
missing values should have (i.e. any op involving a NaN evaluates to a
NaN). If I say
Thanks to Bill Gould and Kit Baum for their very informative answers to my
query. If Stata ever decides to go over to supporting NaNs, then it looks
like it would be a good idea also to support +Inf and -Inf as well, because
these often appear in applied statistics as confidence limits (eg for odds
ratios and Hodges-Lehmann median differences).
g byte badrep = (rep78>3)
I get 5 obs of badrep=1 corresponding to rep78==. whereas in true NaN
arithmetic they would be discarded as having no defined value. (As the
IEEE std says, there are differences between three constructs, none of
which can be represented in finite arithmetic: NaN, +Inf, and -Inf). To do
this right in Stata, I would have to say
g byte badrep = (rep78>3 & rep78<.)
and forgetting the second clause will bite you (well, in this case maybe
Most lower-level programming languages (and some higher-level languages,
e.g. Mathematica, MATLAB) support NaNs per the IEEE standard. Stata does
not--it allows missing values to be treated as a very large positive
number--and that has been the topic of discussion at 'wishes and grumbles'
sessions at SUG meetings.
I don't know whether Bill Gould is saying that tabstat's 'magic number'
behavior is inappropriate, but it is established and well defined. Nick
Cox and I mimicked it in statsmat. It is very useful to be able to
indicate that a certain matrix cell is not zero but rather not defined.
Lecturer in Medical Statistics
Department of Public Health Sciences
King's College London
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Opinions expressed are those of the author, not the institution.
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