Frequencies for first 10,000 rows of dmage variable in natl1988 dataset :

     Age of |
     Mother |      Freq.     Percent        Cum.
------------+-----------------------------------
         13 |         11        0.11        0.11
         14 |         42        0.42        0.53
         15 |        115        1.15        1.68
         16 |        241        2.41        4.09
         17 |        375        3.75        7.84
         18 |        502        5.02       12.86
         19 |        584        5.84       18.70
         20 |        623        6.23       24.93
         21 |        588        5.88       30.81
         22 |        642        6.42       37.23
         23 |        698        6.98       44.21
         24 |        682        6.82       51.03
         25 |        666        6.66       57.69
         26 |        604        6.04       63.73
         27 |        540        5.40       69.13
         28 |        514        5.14       74.27
         29 |        517        5.17       79.44
         30 |        417        4.17       83.61
         31 |        375        3.75       87.36
         32 |        321        3.21       90.57
         33 |        240        2.40       92.97
         34 |        201        2.01       94.98
         35 |        152        1.52       96.50
         36 |        114        1.14       97.64
         37 |         88        0.88       98.52
         38 |         59        0.59       99.11
         39 |         33        0.33       99.44
         40 |         28        0.28       99.72
         41 |         17        0.17       99.89
         42 |          6        0.06       99.95
         43 |          3        0.03       99.98
         44 |          1        0.01       99.99
         48 |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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