Frequencies for first 10,000 rows of f_rf_ppb variable in natl2011 dataset :

   Previous |
    Preterm |
      Birth |
(rf_ppterm) |
          R |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,984       99.84       99.84
          1 |         16        0.16      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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