Year	% of revenue
1972	4.772058076962136
1973	4.432335718932981
1974	5.4272195936543355
1975	5.408868092691631
1976	5.78215672358369
1977	5.24388096495862
1978	5.522439387860352
1979	7.270897687915361
1980	8.906211286664519
1981	10.49416620895122
1982	5.952203393719679
1983	7.222087144617814
1984	13.056286549707588
1985	15.16746758107748
1986	16.315022432203346
1987	18.240470879398256
1988	20.99925815233787
1989	24.14456686167154
1990	35.08650572221331
1997	22.559985148744605
1998	20.125488582596173
1999	19.635771110898112
2000	16.611083271414007
2001	16.077359186822772
2002	14.83632775823931
2003	13.495393528542204
2004	13.05605686968741
2005	12.698307860983052
2006	12.058398766975326
2007	11.926595380761635
2008	12.720127613272625
2009	13.943625432847941
2010	15.33489880353349
2011	17.76540018757005
2012	11.612717096532226
2013	8.808592609888507
2014	9.068100803596934
2015	7.978340671000159
2016	6.99803406049409
2017	6.985215085867151
2018	7.430076067875952
2019	6.703246775941006
2020	6.557728436156397
2021	5.64099647366625
2022	5.433500589728725