Frequencies for first 10,000 rows of rf_ppterm variable in natlterr2015 dataset :

   Previous |
    Preterm |
Birth Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      1,078       10.78       10.78
          N |      8,750       87.50       98.28
          U |         57        0.57       98.85
          Y |        115        1.15      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 20 Oct 2016