Frequencies for first 10,000 rows of pregnant variable in nhamcsed1998 dataset :

 if female, |
 is patient |
  pregnant? |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        307        3.07        3.07
          2 |      3,438       34.38       37.45
          3 |      1,384       13.84       51.29
          4 |      4,871       48.71      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016