Frequencies for first 10,000 rows of popsum variable in nhamcsed1999 dataset :

# of clinic |
   sampling |
   units in |
   hospital |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
         -1 |        244        2.44        2.44
          0 |      9,756       97.56      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016