Frequencies for first 10,000 rows of left variable in nhamcsed1995 dataset :

left before |
 being seen |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,867       98.67       98.67
          1 |        133        1.33      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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