Frequencies for first 10,000 rows of venl30 variable in natl1990 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         42        0.42        0.42
          2 |      9,890       98.90       99.32
          8 |          1        0.01       99.33
          9 |         67        0.67      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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