Frequencies for first 10,000 rows of ob_srvc_cd variable in pos2009 dataset :

       SRV: |
 OBSTETRICS |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      8,638       86.38       86.38
          0 |        743        7.43       93.81
          1 |        562        5.62       99.43
          2 |         36        0.36       99.79
          3 |         21        0.21      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 17 May 2017