Frequencies for first 10,000 rows of ld_chor variable in natl2013 dataset :

Chorioamnio |
  nitis RFP |
613=f_ld_ch |
     orio R |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,749       97.49       97.49
          U |        153        1.53       99.02
          Y |         98        0.98      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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