Frequencies for first 10,000 rows of ip_syph variable in natlterr2014 dataset :

 Syphilis Y |
        Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      1,077       10.77       10.77
          N |      8,792       87.92       98.69
          U |        127        1.27       99.96
          Y |          4        0.04      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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