Frequencies for first 10,000 rows of ld_chor variable in natl2014 dataset :

Chorioamnio |
nitis Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,749       97.49       97.49
          U |         73        0.73       98.22
          Y |        178        1.78      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 15 Jun 2016