Frequencies for first 10,000 rows of venl30 variable in natlterr2000 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         25        0.25        0.25
          2 |      9,973       99.73       99.98
          9 |          2        0.02      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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