Frequencies for first 10,000 rows of preterm variable in natl2002 dataset :

   Previous |
 preterm or |
small-for-g |
estational- |
 age infant |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        204        2.04        2.04
          2 |      9,483       94.83       96.87
          9 |        313        3.13      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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