Frequencies for first 10,000 rows of urf_hydra variable in natl2004 dataset :

Hydramnios/ |
Oligohydram |
     nios U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        195        1.95        1.95
          2 |      8,824       88.24       90.19
          9 |        981        9.81      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 21 Jan 2016