Year	% of revenue
1972	11.91176470588242
1973	8.595242229553692
1974	8.006912442396322
1975	6.59436959141196
1976	6.524919535745625
1977	6.47283126787417
1978	4.9972104885630015
1980	5.934050481614267
1981	6.040643144260821
1982	5.552669852482869
1983	5.920486199037745
1984	5.967375593640307
1985	5.889819751205896
1986	6.770641235049271
1987	6.824202606760603
1988	6.4738056576360945
1989	7.162891949596009
1990	6.961959353830116
1991	7.951541850220263
1992	8.896034297963547
1993	8.494485458947306
1994	12.973275500209835
1995	31.824458146487288
1996	31.584588048255867
1997	32.59430789133247
1998	32.316539840811686
1999	32.42010935601458
2000	33.238314447592074
2001	34.12165058949625
2002	33.20144557293289
2003	33.23683901292597
2004	36.108561681523064
2005	37.151653363740024
2006	37.280513716417204
2007	37.55710306406685
2008	37.04405097938585
2009	36.23974843836315
2010	36.847700811478305
2011	36.21943502824859
2012	34.94630633200228
2013	34.10874759407977
2014	34.56092669639917
2015	33.09093114135561
2016	33.64811637257664
2017	32.74559273250585
2018	33.396583933813716
2019	33.012964784576035
2020	31.013685197817193
2021	30.3992611802459
2022	31.917060467041498