Year	% of revenue
1972	7.6854219948849085
1973	8.723731419784734
1974	8.540549668594597
1975	9.446679734516321
1976	9.616753353408152
1977	9.394176620621726
1978	8.908860017583278
1979	9.834454442211928
1980	9.566302416153057
1981	9.485407066052218
1982	9.63345998914382
1983	8.853714577482746
1984	8.833985869222802
1985	9.388259198023944
1986	10.176659103549964
1987	10.067707305352258
1988	9.251496351163196
1989	8.924436554492159
1990	8.41653561545305
1991	8.272881227409453
1992	9.056925538948256
1993	12.875927928145584
1994	14.062967652814566
1995	33.660558464223385
1996	32.855140963826805
1997	31.587784892311827
1998	31.31105291599119
1999	32.083020247354845
2000	28.77242223061838
2001	30.491891407579967
2002	29.915803333217838
2003	29.97084849843893
2004	29.828867073494298
2005	30.388040712468197
2006	30.855466104883007
2007	30.378252252505515
2008	30.588889340872417
2009	33.66481780948207
2010	33.90879478827362
2011	32.533871120555474
2012	33.56430045886638
2013	33.16262515043659
2014	33.2734222717262
2015	33.51536940052496
2016	33.55230763687895
2017	32.30807465177103
2018	31.98991577379247
2019	31.938989044437733
2020	32.304987399636644
2021	32.6107213623949
2022	32.24472632980587