Year	% of revenue
1973	19.871794871794872
1974	21.04009832539564
1975	19.95473260786351
1976	19.90980752661548
1977	20.45557750011435
1978	21.146232438242723
1979	21.682985289981524
1980	21.99801555681354
1981	22.27925961720113
1982	21.344644784500574
1983	22.543331331840314
1984	22.818713518603044
1985	23.543961532483603
1986	20.893495208362847
1987	21.83595217680323
1988	22.872455939172962
1989	24.253606311442308
1990	21.389499970271693
1991	23.05249447855739
1992	18.40582141794606
1993	20.509173841738427
1994	20.144188306624194
1995	22.280653272965075
1996	23.32594372824729
1997	23.18361560315873
1998	23.293044680818248
1999	24.24430675669048
2000	24.508575085268745
2001	23.498984877338653
2002	22.37341589239049
2003	22.7364045722203
2004	20.768108251525604
2005	20.947455855952413
2006	20.79028771572405
2007	22.417645690959922
2008	22.757066745030343
2009	20.154076948238718
2010	17.838532930783852
2011	17.511834467992575
2012	18.470496724348845
2013	19.91426891936909
2014	20.39573780312797
2015	20.42179189491361
2016	20.007368244232758
2017	19.72186694326402
2018	20.563258090294813
2019	21.56551152257433
2020	22.12879424386493
2021	22.323362819981924
2022	23.699053661817246