Frequencies for first 10,000 rows of preterm variable in natl1989 dataset :

   Previous |
 preterm or |
small-for-g |
estational- |
 age infant |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         76        0.76        0.76
          2 |      9,721       97.21       97.97
          9 |        203        2.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016