Frequencies for first 10,000 rows of combgest variable in natl2007 dataset :

Gestation - |
  Detail in |
  Weeks U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
         18 |          1        0.01        0.01
         20 |          1        0.01        0.02
         21 |          5        0.05        0.07
         22 |         10        0.10        0.17
         23 |          5        0.05        0.22
         24 |          5        0.05        0.27
         25 |          4        0.04        0.31
         26 |          7        0.07        0.38
         27 |         12        0.12        0.50
         28 |         10        0.10        0.60
         29 |         12        0.12        0.72
         30 |         28        0.28        1.00
         31 |         40        0.40        1.40
         32 |         48        0.48        1.88
         33 |         78        0.78        2.66
         34 |        139        1.39        4.05
         35 |        225        2.25        6.30
         36 |        399        3.99       10.29
         37 |        897        8.97       19.26
         38 |      1,766       17.66       36.92
         39 |      2,432       24.32       61.24
         40 |      2,232       22.32       83.56
         41 |      1,044       10.44       94.00
         42 |        311        3.11       97.11
         43 |        139        1.39       98.50
         44 |         67        0.67       99.17
         45 |         33        0.33       99.50
         46 |         24        0.24       99.74
         47 |         10        0.10       99.84
         99 |         16        0.16      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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