Year	% of revenue
1972	13.667315175097276
1973	12.903225806451612
1974	10.683453237410072
1975	12.520272461887771
1976	13.498975409836063
1977	8.32459635143636
1978	5.7214409554999035
1979	8.676377454084863
1980	6.5089548249131255
1981	5.679978413383703
2003	22.31907282681212
2004	21.271176202013926
2005	22.802862163324246
2006	21.884518052505843
2007	19.7896857883222
2008	23.793544228740945
2009	23.078014716557025
2010	20.96922209180018
2011	19.566861512079154
2012	19.74967749416591
2013	20.389549680397113
2014	18.261591062013196
2015	12.69196932535133
2020	15.656672048581232