Re: st: more bizarre missing observations

[David Kantor <dkantor@jhu.edu>]

At 12:43 PM 10/9/2003 +0100, Kristien Verheyen wrote:
> I have a similar problem to Robert's in that I know for sure there are
> missing data for a particular variable ('canter') but if I type
>
> tab canter if canter==.
>
> I am told there are 'no observations'
>
> canter is stored as float but following Neil's suggestion still gives me 'no
> observations'. Please can anyone tell me how I find out exactly how many
> missing values there are?
> Thank you,
>
> Kristien Verheyen
> [...]
By default, -tabulate- omits missing observations, so the behavior you see 
is completely expected.

If you want to see the missings, then code...

 tab canter if canter==. , mis

which will allow the missings to be shown.

But note that such a tabulation will have only one row: missing (.).  You 
can get the same information by...
 count if canter==.

Another issue to consider is, do you use Stata 8 or an earlier edition?  If 
you have Stata 8, then to test canter==. is to seek a specific missing 
value: .   But there are others: .a, .b, .c, etc..  If you want to get all 
missing values, then you should test...
 missing(canter)
or, equivalently,
 mi(canter)
or, equivalently,
 canter <.

Thus, a tabulation such as
 tab canter if mi(canter), mis
will show you all the different species of missing values.  And
 count if mi(canter)
will just give you the total, regardless of the species.

I hope this helps.
-- David

(The missing() function exists at least as far back as Stata 6.  The mi() 
function, as a synonym for missing() came later -- I'm not sure if it is 
Stata 7 or 8.)

David Kantor
Institute for Policy Studies
Johns Hopkins University
dkantor@jhu.edu
410-516-5404

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