Frequencies for first 10,000 rows of nervous variable in natl2001 dataset :

      Other |
    central |
    nervous |
     system |
  anomalies |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          2        0.02        0.02
          2 |      9,996       99.96       99.98
          8 |          1        0.01       99.99
          9 |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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