Frequencies for first 10,000 rows of f_rf_ppb variable in linkpe2009psden dataset :

   Previous |
    Preterm |
    Birth R |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      3,424       34.24       34.24
          1 |      6,575       65.75       99.99
          3 |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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