Frequencies for first 10,000 rows of combgest variable in natl2013 dataset :

Gestation - |
  Detail in |
  Weeks U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
         18 |          1        0.01        0.01
         20 |          1        0.01        0.02
         21 |          4        0.04        0.06
         22 |          3        0.03        0.09
         23 |          6        0.06        0.15
         24 |          6        0.06        0.21
         25 |          2        0.02        0.23
         26 |         12        0.12        0.35
         27 |         13        0.13        0.48
         28 |         10        0.10        0.58
         29 |         25        0.25        0.83
         30 |         26        0.26        1.09
         31 |         29        0.29        1.38
         32 |         42        0.42        1.80
         33 |         84        0.84        2.64
         34 |        134        1.34        3.98
         35 |        221        2.21        6.19
         36 |        366        3.66        9.85
         37 |        897        8.97       18.82
         38 |      1,585       15.85       34.67
         39 |      2,611       26.11       60.78
         40 |      2,108       21.08       81.86
         41 |      1,135       11.35       93.21
         42 |        344        3.44       96.65
         43 |        151        1.51       98.16
         44 |         78        0.78       98.94
         45 |         34        0.34       99.28
         46 |         32        0.32       99.60
         47 |         22        0.22       99.82
         99 |         18        0.18      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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