Frequencies for first 10,000 rows of vacuum variable in natl1990 dataset :

     Vacuum |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        471        4.71        4.71
          2 |      9,522       95.22       99.93
          9 |          7        0.07      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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