Frequencies for first 10,000 rows of gestwk variable in nhamcsopd2006 dataset :

       week of |
     gestation |      Freq.     Percent        Cum.
---------------+-----------------------------------
             3 |          2        0.02        0.02
             4 |          2        0.02        0.04
             5 |          8        0.08        0.12
             6 |         19        0.19        0.31
             7 |          9        0.09        0.40
             8 |          9        0.09        0.49
             9 |         11        0.11        0.60
            10 |         13        0.13        0.73
            11 |         10        0.10        0.83
            12 |         15        0.15        0.98
            13 |         13        0.13        1.11
            14 |         16        0.16        1.27
            15 |         13        0.13        1.40
            16 |         15        0.15        1.55
            17 |         17        0.17        1.72
            18 |         12        0.12        1.84
            19 |         14        0.14        1.98
            20 |         16        0.16        2.14
            21 |         29        0.29        2.43
            22 |         16        0.16        2.59
            23 |         12        0.12        2.71
            24 |         16        0.16        2.87
            25 |         18        0.18        3.05
            26 |         14        0.14        3.19
            27 |         17        0.17        3.36
            28 |         13        0.13        3.49
            29 |         25        0.25        3.74
            30 |         21        0.21        3.95
            31 |         26        0.26        4.21
            32 |         26        0.26        4.47
            33 |         22        0.22        4.69
            34 |         30        0.30        4.99
            35 |         33        0.33        5.32
            36 |         45        0.45        5.77
            37 |         45        0.45        6.22
            38 |         32        0.32        6.54
            39 |         32        0.32        6.86
            40 |          5        0.05        6.91
            41 |          3        0.03        6.94
            44 |          1        0.01        6.95
Not applicable |      8,182       81.82       88.77
         Blank |      1,123       11.23      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016