Frequencies for first 10,000 rows of f_rf_ppb variable in natl2007 dataset :

   Previous |
    Preterm |
      Birth |
(rf_ppterm) |
          R |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,994       99.94       99.94
          1 |          6        0.06      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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