Year	% of revenue
1972	23.60091635887606
1973	24.977453472165287
1974	26.197680282400405
1975	28.107533518499466
1976	28.274287918729506
1977	27.876976111604858
1978	28.261756727560794
1979	27.71888174859809
1980	28.22415182824064
1981	27.99512339986558
1982	29.852488591743604
1983	31.31237372191269
1984	32.68598953112819
1985	32.90416324467749
1986	33.915705833039716
1987	32.81857949924161
1988	34.233354457338166
1989	33.90760116573504
1990	26.099096188941736
1991	26.27480959365934
1992	28.04360062296601
1993	27.91452721309663
1994	28.372095775937794
1995	27.55236137833645
1996	26.698889292263544
1997	25.92065577734671
1998	25.63637405240774
1999	25.731704115137582
2000	25.061794024563973
2001	27.65478088353376
2002	30.409102709771854
2003	30.898339262798054
2004	30.41871341508766
2005	28.960258181449724
2006	28.00130504572733
2007	28.04246022931195
2008	29.427231556164827
2009	32.568961771454475
2010	31.16880291960691
2011	28.648607511568052
2012	28.834718269490274
2013	29.125400582040747
2014	28.88296758224218
2015	28.759026648491968
2016	29.156143151630314
2017	27.945892912665112
2018	29.2631996466798
2019	29.94961654000267
2020	29.993631225100522
2021	28.29235016260231
2022	28.198455033799974