Frequencies for first 10,000 rows of venl30 variable in natl1998 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        120        1.20        1.20
          2 |      9,877       98.77       99.97
          9 |          3        0.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 22 Dec 2015