Frequencies for first 10,000 rows of chromo variable in natl1989 dataset :

      Other |
chromosomal |
  anomalies |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          4        0.04        0.04
          2 |      9,759       97.59       97.63
          9 |        237        2.37      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016