Year	% of revenue
1972	7.906655407998772
1973	8.169977634521773
1974	7.717093603995489
1975	7.931018582560981
1976	9.392505102262366
1977	9.579618813403012
1978	10.161255489165647
1979	9.445074326026708
1980	13.109472327629412
1981	15.165130568356375
1982	16.664709336465062
1983	18.267443824970435
1984	16.143777269894034
1985	12.774329416980715
1986	12.184863238930383
1987	12.170360282283026
1988	13.917270929466053
1989	13.962156705407294
1990	22.87716684723727
1991	28.914638170419067
1992	29.458333716450436
1993	31.30805402137171
1994	28.72103630969628
1995	27.283505859820327
1996	28.462801058520082
1997	26.481820408986756
1998	32.00639837132366
1999	36.43202797771543
2000	35.71949652033951
2001	36.58936098512262
2002	35.321202544873884
2003	32.586382681913825
2004	31.389791576598657
2005	33.165209569180995
2006	32.795306977322895
2007	31.343967677417872
2008	31.34811835901172
2009	33.65374069464649
2010	30.469201788513452
2011	28.939807842592234
2012	27.89918637889472
2013	28.03921789275437
2014	26.85760637079449
2015	24.61135336103613
2016	29.55473783239851
2017	32.45023094169769
2018	38.064810780743024
2019	37.78031428624684
2020	39.38341511814626
2021	37.18133117239147
2022	34.30345866414584