Year	% of revenue
1972	19.752424843255987
1973	27.19835924208171
1974	26.879219957978904
1975	27.17061704914503
1976	25.507009663808354
1977	25.63672060117798
1978	25.742550309597522
1979	25.497394599715772
1980	21.893632041370044
1981	21.60878472739131
1982	22.165539118894248
1983	21.005208509869053
1984	20.7471202387005
1985	20.17245686347983
1986	21.586760967342418
1987	22.8872375955127
1988	23.951985566213153
1989	25.190549451323196
1990	23.50431590435559
1991	23.833704666419113
1992	25.005628799439624
1993	23.474838689994968
1994	22.875714330592626
1995	23.250815371879394
1996	22.09339189078341
1997	22.209767748141633
1998	24.629652084108596
1999	23.64907091662178
2000	18.6489222798651
2001	19.586443704288705
2002	20.79223458899436
2003	21.018011719761635
2004	19.55411225117924
2005	18.054473097245292
2006	16.86130453545304
2007	17.409178232357338
2008	16.862874772944227
2009	20.210887804473373
2010	19.958045708268887
2011	19.01227705102089
2012	19.25012339645186
2013	20.528173518758926
2014	21.63187908124918
2015	22.9575547528485
2016	23.564236461319478
2017	22.720642766379502
2018	21.505482025727616
2019	22.18054755245738
2020	24.769179068091447
2021	19.705779580307524
2022	13.43572683321156