Frequencies for prolong variable in linkco1995us_unl dataset :

  Prolonged |
 labor (>20 |
     hours) |      Freq.     Percent        Cum.
------------+-----------------------------------
          . |        708      100.00      100.00
------------+-----------------------------------
      Total |        708      100.00

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