Frequencies for first 10,000 rows of nhs variable in accident dataset :

        nhs |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      6,724       67.24       67.24
          1 |      3,266       32.66       99.90
          9 |         10        0.10      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 18 Apr 2016