Frequencies for first 10,000 rows of venl30 variable in natl1997 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         83        0.83        0.83
          2 |      9,904       99.04       99.87
          8 |          1        0.01       99.88
          9 |         12        0.12      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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