Frequencies for first 10,000 rows of nocharge variable in nhamcsopd1993 dataset :

   expected |
  source of |
 payment-no |
     charge |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,743       97.43       97.43
          1 |        257        2.57      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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