Frequencies for first 10,000 rows of rf_phyp variable in natlterr2007 dataset :

Prepregnanc |
          y |
Hypertensio |
      n RFP |
584=f_rf_ph |
     yper R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,163       61.63       61.63
          N |      3,783       37.83       99.46
          U |          1        0.01       99.47
          Y |         53        0.53      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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