Frequencies for first 10,000 rows of venl30 variable in natl1989 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         45        0.45        0.45
          2 |      9,765       97.65       98.10
          9 |        190        1.90      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016