Year	% of revenue
1972	28.13865013385938
1973	27.325380359612723
1974	25.662724306688418
1975	24.537627551020407
1976	24.848210240144994
1977	25.20589466967117
1978	25.64135197541863
1979	26.2071324192395
1980	28.465449390139568
1981	27.862516914749662
1982	28.578609794922876
1983	29.531160411061613
1984	30.51432715525411
1985	31.031063125400777
1986	32.045598932122694
1987	30.435275750256867
1988	31.19302322795501
1989	30.38931726327142
1990	28.35360283624908
1991	29.27766745065022
1992	31.150871197316874
1993	32.21582195282261
1994	33.01066205908382
1995	34.28361278198384
1996	34.79034011774845
1997	35.02778434010908
1998	34.40400006289407
1999	35.19442622074849
2000	34.23806427437842
2001	33.644757646293435
2002	35.00952593229424
2003	35.307887164978325
2004	34.19394619353822
2005	32.01929188002304
2006	32.33185852398479
2007	32.23017224190555
2008	30.12898506575119
2009	30.900971724877003
2010	28.545681476160606
2011	34.78478028868439
2012	34.496396570013836
2013	34.68184793525531
2014	35.78208191293605
2015	35.55608748236242
2016	35.24590163934426
2017	34.73630401997278
2018	34.71199366053477
2019	34.985213226081356
2020	33.16388924894191
2021	32.66128579747299
2022	32.18545402480877