Frequencies for first 10,000 rows of clingest variable in natl2002 dataset :

   Clinical |
Estimate of |
  Gestation |      Freq.     Percent        Cum.
------------+-----------------------------------
         19 |          1        0.01        0.01
         20 |          1        0.01        0.02
         21 |          3        0.03        0.05
         22 |          1        0.01        0.06
         23 |          3        0.03        0.09
         24 |          8        0.08        0.17
         25 |          3        0.03        0.20
         26 |          6        0.06        0.26
         27 |         10        0.10        0.36
         28 |         12        0.12        0.48
         29 |         13        0.13        0.61
         30 |         15        0.15        0.76
         31 |         22        0.22        0.98
         32 |         38        0.38        1.36
         33 |         68        0.68        2.04
         34 |        112        1.12        3.16
         35 |        185        1.85        5.01
         36 |        369        3.69        8.70
         37 |        719        7.19       15.89
         38 |      1,606       16.06       31.95
         39 |      2,547       25.47       57.42
         40 |      2,928       29.28       86.70
         41 |      1,058       10.58       97.28
         42 |        210        2.10       99.38
         43 |          7        0.07       99.45
         99 |         55        0.55      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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