Frequencies for first 10,000 rows of birmon variable in natl1980 dataset :

   Month of |
      birth |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      4,773       47.73       47.73
          2 |      3,878       38.78       86.51
          3 |      1,349       13.49      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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