Frequencies for first 10,000 rows of urf_preterm variable in natl2005 dataset :

   Previous |
 Preterm or |
  Small for |
Gestation U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        234        2.34        2.34
          2 |      9,643       96.43       98.77
          9 |        123        1.23      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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