Frequencies for first 10,000 rows of nervous variable in linkco1991us_num dataset :

      Other |
    central |
    nervous |
     system |
  anomalies |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         48        0.48        0.48
          2 |      9,679       96.79       97.27
          9 |        273        2.73      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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