Frequencies for first 10,000 rows of ld_chor variable in natl2016 dataset :

Chorioamnio |
nitis Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,758       97.58       97.58
          U |         34        0.34       97.92
          Y |        208        2.08      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 4 Oct 2017