Frequencies for first 10,000 rows of monprec variable in natl1981 dataset :

     Detail |
      Month |
   Prenatal |
 Care began |      Freq.     Percent        Cum.
------------+-----------------------------------
          - |         73        0.73        0.73
          0 |        142        1.42        2.15
          1 |      1,053       10.53       12.68
          2 |      3,734       37.34       50.02
          3 |      2,315       23.15       73.17
          4 |      1,131       11.31       84.48
          5 |        672        6.72       91.20
          6 |        439        4.39       95.59
          7 |        229        2.29       97.88
          8 |        148        1.48       99.36
          9 |         64        0.64      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016