Frequencies for ptype variable in impact2009 dataset :

   Provider |
       Type |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      2,756       76.15       76.15
          7 |        196        5.42       81.57
          8 |         35        0.97       82.54
         14 |        157        4.34       86.87
         15 |         12        0.33       87.21
         16 |        356        9.84       97.04
         17 |        104        2.87       99.92
         21 |          3        0.08      100.00
------------+-----------------------------------
      Total |      3,619      100.00

by Jean Roth , jroth@nber.org , 17 Mar 2016