Year	% of revenue
1974	21.033891599630753
1975	22.789406236651004
1976	21.591018136455233
1977	20.238816301808427
1978	18.745223903408224
1979	18.684174531527834
1980	17.772207617533777
1981	18.743951510212398
1982	17.79390934844193
1983	17.15451620497528
1984	15.674456192336184
1985	15.035013424119128
1986	14.375833174633405
1987	13.874296238933423
1988	15.5135929990675
1989	14.465231935111452
1990	14.837958793454616
1991	17.256806407121083
1992	17.77098647605897
1993	19.60539017711145
1994	21.622849724115547
1995	22.50551473075934
1996	22.405477890058233
1997	20.615916098516443
1998	23.51393734452339
1999	24.61901034649421
2000	27.014495291617248
2001	26.734173673821477
2002	28.454093823595137
2003	31.50188647530773
2004	34.06766366329174
2005	35.933568193256164
2006	39.49833951257226
2007	43.920942894282106
2008	45.22831034067824
2009	50.27095205032025
2010	43.38476173489105
2011	48.384377885216765
2012	44.838910034877614
2013	46.57921277391053
2014	47.67311651609305
2015	42.85594103598319
2016	42.46947761439105
2017	45.77204650500989
2018	45.64661902426044