Year	% of tax revenue
1972	0.015306903413439503
1973	0.02421014405035713
1974	0.020820320632937744
1975	0.01721318529993977
1976	0.01869741352446246
1977	0.01612123166209899
1978	0.021522038567493025
1979	0.02139647671350113
1980	0.020982584454902403
1981	0.002797985450475665