Year	% of revenue
1972	11.22302158273382
1973	11.401425178147239
1974	11.715481171548065
1975	13.482216708023193
1976	14.18047882136278
1977	15.312984997413345
1978	16.932624113475185
1979	17.375366568914938
1980	16.92957746478875
1981	18.68082222724186
1982	21.098626716604223
1983	20.702885205647682
1984	21.11853088480803
1985	23.497979929623313
1986	22.557146445616773
1987	21.943573667711654
1988	20.799567801188466
1989	20.83288496717961
1990	22.186957599801683
1991	20.6523837097086
1992	19.062768701633715
1993	17.856161968046735
1994	16.35117848354141
1995	14.48793413351652
1996	12.387428593893171
1997	10.636686028012074
1998	9.896680562314836
1999	7.025391070449065
2000	5.795898881258699
2001	4.564104138094003
2002	4.308263823603901
2003	3.948965693870394
2004	3.4447148451377814
2005	3.1262864950583635
2006	2.9166436371262145
2007	3.0080288420250305
2008	3.9893869295576248
2009	6.4822884160940735
2010	9.119655158771131
2011	10.487409760978531
2012	12.824906578771
2013	13.21012289414669
2014	11.923044447436002
2015	10.138266841158899
2016	8.826039303811427
2017	7.977850482944832
2018	6.630281580874575
2019	5.432276405821463
2020	4.7325969245600445
2021	3.4126059701058606
2022	2.959561570914396