Year	% of revenue
1974	10.338915996307529
1975	10.273387441264417
1976	11.467229632472892
1977	11.594704508090334
1978	12.777013602323093
1979	12.925728354534263
1980	13.780033013388762
1981	14.073244027912187
1982	15.563031161473088
1983	17.460566585576395
1984	19.01138123779379
1985	19.624124664397023
1986	20.586554941915825
1987	22.398961887021496
1988	23.934796642995483
1989	24.459015422870845
1990	27.63914483255511
1991	28.92360829402288
1992	29.499857856475654
1993	33.97427057270632
1994	33.637617656605
1995	31.889353524691106
1996	32.15118883478483
1997	32.94177155248955
1998	37.40530931863574
1999	37.157986133388086
2000	38.91241532473115
2001	40.93629058580333
2002	39.46951334811683
2003	36.05854226635171
2004	31.90673024326305
2005	28.57095348842365
2006	25.638980162007346
2007	23.37026401659557
2008	26.538502374767305
2009	28.46290689027572
2010	22.825787528364895
2011	22.86838944097529
2012	24.9086652545747
2013	25.689157833118227
2014	27.18508476239061
2015	25.209617640598054
2016	24.210560884359754
2017	24.29193689786064
2018	23.011306254749012