Frequencies for first 10,000 rows of rf_phyp variable in linkpe2009psden dataset :

Prepregnanc |
          y |
Hypertensio |
        n R |
(f_rf_phype |
r rep flag) |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      3,422       34.22       34.22
          N |      6,482       64.82       99.04
          U |          1        0.01       99.05
          Y |         95        0.95      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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