Frequencies for first 10,000 rows of estgest variable in natlterr2005 dataset :

Obstetric/C |
    linical |
  Gestation |
   Est. U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
          9 |          1        0.01        0.01
         16 |          1        0.01        0.02
         17 |          1        0.01        0.03
         19 |          1        0.01        0.04
         20 |          2        0.02        0.06
         21 |          5        0.05        0.11
         22 |          3        0.03        0.14
         23 |          8        0.08        0.22
         24 |          8        0.08        0.30
         25 |          5        0.05        0.35
         26 |         15        0.15        0.50
         27 |         17        0.17        0.67
         28 |         17        0.17        0.84
         29 |         19        0.19        1.03
         30 |         32        0.32        1.35
         31 |         23        0.23        1.58
         32 |         55        0.55        2.13
         33 |        108        1.08        3.21
         34 |        142        1.42        4.63
         35 |        261        2.61        7.24
         36 |        440        4.40       11.64
         37 |      1,044       10.44       22.08
         38 |      1,931       19.31       41.39
         39 |      2,016       20.16       61.55
         40 |      1,423       14.23       75.78
         41 |        514        5.14       80.92
         42 |        108        1.08       82.00
         43 |         27        0.27       82.27
         44 |         17        0.17       82.44
         45 |          3        0.03       82.47
         46 |          5        0.05       82.52
         47 |          3        0.03       82.55
         99 |      1,745       17.45      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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