Frequencies for first 10,000 rows of rf_ppterm variable in natl2013 dataset :

   Previous |
    Preterm |
  Birth RFP |
587=f_rf_pp |
        b R |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,424       94.24       94.24
          U |        167        1.67       95.91
          Y |        409        4.09      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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