Frequencies for first 10,000 rows of popsum variable in nhamcsopd1994 dataset :

# of clinic |
   sampling |
   units in |
   hospital |      Freq.     Percent        Cum.
------------+-----------------------------------
         -1 |      6,808       68.08       68.08
          0 |      3,192       31.92      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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