Frequencies for first 10,000 rows of venl30 variable in natl1994 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         35        0.35        0.35
          2 |      9,909       99.09       99.44
          9 |         56        0.56      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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