Frequencies for first 10,000 rows of proc52d variable in namcs2012 dataset :

Procedure 5 |
  - 2 digit |      Freq.     Percent        Cum.
------------+-----------------------------------
         -9 |      9,995       99.95       99.95
         89 |          1        0.01       99.96
         90 |          3        0.03       99.99
         99 |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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