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

   Previous |
    Preterm |
    Birth R |
  (f_rf_ppb |
  rep flag) |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      3,422       34.22       34.22
          N |      6,485       64.85       99.07
          U |          1        0.01       99.08
          Y |         92        0.92      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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