Frequencies for first 10,000 rows of rf_ppterm variable in natlterr2011 dataset :

   Previous |
    Preterm |
  Birth RFP |
587=f_rf_pp |
        b R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      2,536       25.36       25.36
          N |      6,295       62.95       88.31
          U |      1,074       10.74       99.05
          Y |         95        0.95      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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