Year	% of revenue
1972	4.219409282700422
1973	4.215851602023609
1974	4.329608938547486
1975	3.860294117647059
1976	4.105775922059847
1977	4.226859283039058
1978	3.63761153054221
1979	3.241393195087578
1980	3.395747381783561
1981	5.687564946311049
1983	5.451862140810834
1984	5.604926435340536
1985	9.770770666943262
1986	4.25700521649896
1987	4.145606485091799
1988	3.348480951156078
1989	3.0746203598648747
1990	2.8877132970048924
1991	2.6395161208480062
1992	2.4889009234657324
1993	2.451926594146215
1994	6.2093067212527995
1995	3.2836991491282705
1996	2.238510856493607
1997	3.5833893669597425
1998	3.708299111061782
2008	2.7525458348138314
2009	3.1578869439152295
2010	2.8420261625840704
2011	2.652493001536382
2012	2.5481188454496637
2013	0.9641179718484607
2014	1.842406151817878
2015	1.8742898392486587
2016	1.8385440849229842
2017	1.8657826993983007
2018	1.6729830411450715
2019	1.696834318810017
2020	1.5765593997414233
2021	1.5329341479040735
2022	1.4461691046131775