Year	% of revenue
1972	20
1973	15.789473684210526
1974	19.230769230769234
1975	16.666666666666664
1976	20.967741935483872
1977	22.22222222222222
1978	24.305555555555554
1979	21.639344262295083
1980	20.516499282639884
1981	20.759493670886076
1982	26.114315679077084
1983	22.457818280249032
1984	21.283282107953173
1985	21.492297924950712
1986	23.443674021949022
1987	25.440398362743643
1988	27.85072463346267
1989	26.88343888158681
1990	28.348406546080962
1991	31.865587675263978
1992	32.82068288908234
1993	32.33591560499811
1994	32.250274651244744
1995	31.401916553002486
1996	30.36439023320097
1997	29.36498304023712
1998	28.572258803154547
1999	29.190788835343962
2000	27.705131459456233
2001	27.405865516482514
2002	28.950045531916363
2003	29.939018614641277
2004	30.740820517334672
2005	30.806060683448273
2006	29.421044373201678
2007	30.570938996463443
2008	32.168716293740374
2009	34.36556009528032
2010	34.99043070304813
2011	34.82008529002237
2012	34.400494876940684
2013	34.91025269616291
2014	35.55310023443133
2015	34.835595031476785
2016	34.80677462543138
2017	32.23134752492772
2018	33.59616580345982
2019	33.482567099447145
2020	33.23172335731756
2021	33.172999364040095
2022	32.018102468585816