Frequencies for first 10,000 rows of preterm variable in linkco1991us_num dataset :

   Previous |
 preterm or |
small-for-g |
estational- |
 age infant |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        323        3.23        3.23
          2 |      9,389       93.89       97.12
          8 |          9        0.09       97.21
          9 |        279        2.79      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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