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st: Weighted number of observations


From   Friedrich Huebler <[email protected]>
To   [email protected]
Subject   st: Weighted number of observations
Date   Fri, 30 Jul 2004 10:35:23 -0700 (PDT)

I am working with binary variables that take the values 0 or 1. I
would like to generate the weighted number of observations that are
equal to 1. The number obtained with -tabstat- is different from that
obtained with -tab- or -collapse-. How can this difference be
explained?

. sysuse auto, clear
. label drop origin
. tab foreign

   Car type |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |         52       70.27       70.27
          1 |         22       29.73      100.00
------------+-----------------------------------
      Total |         74      100.00

. tabstat foreign, stat(sum)

    variable |       sum
-------------+----------
     foreign |        22
------------------------

So far, so good, the unweighted number of observations=1 is the same.
Now let's add a weight.

. tab foreign [aw=weight]

   Car type |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 | 57.1261189       77.20       77.20
          1 | 16.8738811       22.80      100.00
------------+-----------------------------------
      Total |         74      100.00

. tabstat foreign [aw=weight], stat(sum)

    variable |       sum
-------------+----------
     foreign |     50950
------------------------

According to -tab-, the weighted number of observations=1 is about
16.9. According to -tabstat-, the number is 50950. With -collapse- we
get the same result as with -tab-.

. collapse (sum) foreign [aw=weight]
. clist, noobs

 foreign
 16.8739

Should the results obtained with -tab-, -tabstat-, and -collapse- not
be the same? Many thanks for your comments.

Friedrich Huebler


		
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