Year	% of revenue
1972	2.527075812274368
1973	2.5454545454545454
1974	1.3201320132013201
1975	2.247191011235955
1976	0.8954154727793696
1977	1.4634146341463417
1978	3.809937708242793
1979	2.974714923153198
1980	1.6031575869798265
1981	1.403412217941662
1982	4.7257322328537
1983	5.719349926354944
1984	10.54969661947414
1985	10.244815219086231
1986	8.176209447922595
1987	6.874017345437947
1988	6.833153922500518
1989	9.027777777777777
1990	7.944465869649055
1991	6.871955462769659
1992	6.050404001539054
1993	4.878048780487805
1994	6.127795284559019
1995	5.9390998135708575
1996	4.400529918304262
1997	5.030046366816759
1998	4.867237778630184
1999	7.194683251021279
2000	7.786548506367745
2001	8.875159265945848
2002	14.781605296813732
2003	21.068791924588815
2004	18.536856903243013
2005	16.03243118503114
2006	15.415769829132575
2007	14.236658631617788
2008	10.857353176290317
2009	9.331495244139845
2010	7.949318151811109
2011	8.08178745392087
2012	7.755264446035135
2013	7.635088574884892
2014	7.379529587057286
2015	7.570108436969179
2016	7.422006368761018
2017	8.300765634564788
2018	8.237022965538825
2019	7.763086224888989
2020	8.795608395041837