Year	% of revenue
1972	12.16367143872474
1973	13.12621990891348
1974	16.511271917617577
1975	13.324420677361854
1976	16.390431261219824
1977	14.167987321711594
1978	15.128675416977078
1979	16.222035008892558
1980	17.389315595875708
1981	15.4524724954644
1982	19.136999346037793
1983	16.360785760398404
1984	17.937865497076015
1985	17.70664799207938
1986	18.027204404522614
1987	17.49637722454698
1988	18.024768483187696
1989	18.917923934724747
1990	20.419090953343595
1995	17.271288382399494
1996	16.08617594254937
1997	17.002366918828606
1998	19.841596379345813
1999	20.659445988689733
2000	21.879697948886317
2001	19.8933208091516
2002	20.716434061649615
2003	19.3740574278419
2004	19.179742929174644
2005	21.26864192964612
2006	19.539072076117428
2007	18.95366416172852
2008	18.626467077254624
2009	20.154076948238718
2010	17.838532930783852
2011	17.100898963789827
2012	18.728290346777452
2013	16.362150487420465
2014	18.893843230285793
2015	17.78845567520763
2016	18.51536038276605
2017	18.634007691021566
2018	19.27208894090111
2019	17.536317990656926
2020	16.973685869551513
2021	17.256284836764873
2022	17.452971633048797