Frequencies for first 10,000 rows of venl30 variable in natl1991 dataset :

   Assisted |
ventilation |
- less than |
 30 minutes |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         38        0.38        0.38
          2 |      9,932       99.32       99.70
          8 |          1        0.01       99.71
          9 |         29        0.29      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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