Year	% of revenue
1972	18.96551724137931
1973	19.11764705882353
1974	18.947368421052634
1975	17.91044776119403
1976	18.823529411764707
1977	18.25726141078838
1978	17.080745341614907
1979	16.173120728929387
1980	12.481426448736999
1981	13.615560640732266
1982	12.350597609561753
1983	9.939148073022313
1984	9.857942315970728
1985	10.48298572996707
1986	11.355845046280425
1987	11.08035915424967
1988	12.208240809277077
1989	11.59647224077187
1990	12.547340542926506
1991	13.35796021484831
1992	13.708482937877854
1993	15.20904220371666
1994	15.886107251360071
1995	13.880863600136628
1996	12.601725429796446
1997	12.353993880732004
1998	11.585588570493334
1999	10.884668097663145
2000	10.477288988675335
2008	9.502937782633884
2009	11.692807854611944
2010	11.479818539618682
2011	10.902230524031161
2012	11.13776703092803
2013	11.49970457291708
2014	11.79007902054479
2015	11.554578522715817
2016	10.914139643601041
2017	10.666079646912692
2018	11.483358199862108
2019	11.865767431930783
2020	12.824008804414774
2021	12.499219354345783
2022	11.978003454467183