Frequencies for first 10,000 rows of preterm variable in natlterr1998 dataset :

   Previous |
 preterm or |
small-for-g |
estational- |
 age infant |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         12        0.12        0.12
          2 |      9,986       99.86       99.98
          9 |          2        0.02      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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