Frequencies for first 10,000 rows of hydra variable in linkco1991us_num dataset :

Hydramnios/ |
Oligohydram |
       nios |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        342        3.42        3.42
          2 |      9,370       93.70       97.12
          8 |          9        0.09       97.21
          9 |        279        2.79      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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