Frequencies for first 10,000 rows of paydk variable in nhamcsed2006 dataset :

    unknown |
  source of |
    payment |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,672       96.72       96.72
          1 |        328        3.28      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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