Frequencies for first 10,000 rows of estgest variable in natlterr2003 dataset :

Obstetric/C |
    linical |
  Gestation |
  Est. U;R  |      Freq.     Percent        Cum.
------------+-----------------------------------
         21 |          1        0.01        0.01
         22 |          3        0.03        0.04
         23 |          2        0.02        0.06
         24 |          6        0.06        0.12
         25 |         11        0.11        0.23
         26 |          8        0.08        0.31
         27 |         17        0.17        0.48
         28 |         20        0.20        0.68
         29 |         12        0.12        0.80
         30 |         27        0.27        1.07
         31 |         31        0.31        1.38
         32 |         84        0.84        2.22
         33 |         82        0.82        3.04
         34 |        149        1.49        4.53
         35 |        263        2.63        7.16
         36 |        690        6.90       14.06
         37 |      1,556       15.56       29.62
         38 |      2,868       28.68       58.30
         39 |      2,319       23.19       81.49
         40 |      1,619       16.19       97.68
         41 |        204        2.04       99.72
         42 |         21        0.21       99.93
         99 |          7        0.07      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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