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Re: st: the -missing- command


From   "Svend Juul" <SJ@SOCI.AU.DK>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: the -missing- command
Date   Mon, 10 Oct 2005 20:06:00 +0200

Louis wrote:

I'm not clear about exactly what -missing- does. An example will clarify
my concern. I have a dataset containing 11 variables (the first is -clust-
and the last is -s11aq13-). One of the variables is -trexpcd-, and the
total number of observations is 4872. I gave the following commands and
had the shown output:
count if mi(trexpcd)
4649
count if mi(clust-s11aq13)
82

My understanding of the online -help- is that -missing- evaluates the
number of observations for which any of the arguments is missing. So, for
the second command, since -trexpcd- is one of the arguments, I expected
the result to be a number which is at least equal to 4649.
--------------------------------------------------------------

hmm! It looks a bit strange. I tried this:

. sysuse auto
(1978 Automobile Data)
. count if missing(rep78)
     5
. count if missing(mpg, rep78, headroom)
     5
. count if missing(rep78-headroom)
     5
. count if missing(mpg-headroom)
     0
. count if missing(mpg-rep78)
     5

According to the documentation -missing()- takes a list of arguments,
separated by commas. The arguments may be variable names, but not in
a variable list form, so mpg-headroom ought to be illegal. Apparently
missing() accepted mpg-headroom, but examined only mpg and headroom,
not the intervening rep78. I checked it both on Stata 8.2 and 9.1; both
versions have the same behavior.

-egen-s rmiss() function (rowmiss() in version 9) takes a variable list
as arguments, and that may be what you need.

Confused?  I am a bit myself.

Svend
_______________________________________________________

Svend Juul
Institut for Folkesundhed, Afdeling for Epidemiologi
(Institute of Public Health, Department of Epidemiology)
Vennelyst Boulevard 6
DK-8000 Aarhus C,  Denmark
Phone, work:  +45 8942 6090
Phone, home:  +45 8693 7796
Fax:          +45 8613 1580
E-mail:       sj@soci.au.dk
_________________________________________________________

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