Frequencies for first 10,000 rows of rf_ppterm variable in natlterr2007 dataset :

   Previous |
    Preterm |
  Birth RFP |
587=f_rf_pp |
        b R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,163       61.63       61.63
          N |      3,793       37.93       99.56
          U |          1        0.01       99.57
          Y |         43        0.43      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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