Frequencies for first 10,000 rows of venl30 variable in natlterr1998 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         11        0.11        0.11
          2 |      9,984       99.84       99.95
          9 |          5        0.05      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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