Frequencies for first 10,000 rows of venl30 variable in natl1993 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         52        0.52        0.52
          2 |      9,885       98.85       99.37
          8 |          1        0.01       99.38
          9 |         62        0.62      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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