Year	% of revenue
1972	19.705119585054156
1973	20.444976471559464
1974	21.04009832539564
1975	19.392651745485136
1976	19.663832180789502
1977	20.961520940261774
1978	20.35754824063568
1979	20.15518245855623
1980	18.5745495548404
1981	17.516001151639934
1982	17.001436213392175
1983	16.850632911392406
1984	16.542694497153697
1985	17.353254299067114
1986	17.371960862689217
1987	17.36365942335333
1988	17.637569751938216
1989	18.077817110040854
1990	16.29070894883934
1991	16.612804074822165
1992	16.39379862713782
1993	15.121326569889973
1994	14.39616500855008
1995	15.927649851930628
1996	15.665301821362526
1997	15.454876617331589
1998	15.844591681755174
1999	16.409801883604228
2000	17.108973373774
2001	15.198144992247284
2002	14.763578354395673
2003	14.401366528796547
2004	14.4147480576311
2005	14.754663706609477
2006	15.858803053535214
2007	16.736082637375286
2008	17.060677975129977
2009	15.455700182000939
2010	14.959534124702822
2011	15.393681704596105
2012	16.09640737277509
2013	16.454260078601973
2014	16.483479878798114
2015	16.79495869299789
2016	17.34176046728109
2017	17.714533070702
2018	17.96269651380335
2019	17.83907708134323
2020	17.278068857753848
2021	17.567004778082726
2022	18.0140127174391