Frequencies for first 10,000 rows of ven30m variable in natlterr2000 dataset :

   Assisted |
ventilation |
       - 30 |
 minutes or |
       more |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         27        0.27        0.27
          2 |      9,971       99.71       99.98
          9 |          2        0.02      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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