Frequencies for first 10,000 rows of corrlens variable in namcs1995 dataset :

 corrective |
     lenses |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,993       99.93       99.93
          1 |          7        0.07      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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