Frequencies for first 10,000 rows of popsum variable in nhamcsopd1992 dataset :

# of clinic |
   sampling |
   units in |
        hos |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
         -1 |      7,072       70.72       70.72
          0 |      2,928       29.28      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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