Frequencies for first 10,000 rows of venl30 variable in natl2002 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        379        3.79        3.79
          2 |      9,252       92.52       96.31
          9 |        369        3.69      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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