Frequencies for preterm variable in linkco1995us_unl dataset :

   Previous |
 preterm or |
small-for-g |
estational- |
 age infant |      Freq.     Percent        Cum.
------------+-----------------------------------
          . |        708      100.00      100.00
------------+-----------------------------------
      Total |        708      100.00

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