Frequencies for first 10,000 rows of ld_chor variable in natl2017 dataset :

Chorioamnio |
nitis Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,812       98.12       98.12
          U |         31        0.31       98.43
          Y |        157        1.57      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 19 Sep 2018