Year	% of revenue
1972	15.384615384615385
1973	25
1974	28.35820895522388
1975	23.595505617977526
1976	16.666666666666664
1977	15.09433962264151
1978	12.547528517110266
1979	18.148820326678766
1980	25.90775269872424
1981	15.627051871306632
1982	14.929577464788732
1983	11.717495987158909
1984	9.786476868327403
1985	9.344490934449093
1986	21.537474275851388
1987	19.76092978441527
1988	21.339950372208435
1989	16.762234964661953
1990	5.4373973245716964
1991	6.726861085655759
1992	10.966165611659923
1993	13.341651919363487
1994	15.412085548248278
1995	14.922629225149192
1996	18.41121681724805
1997	18.552242360648492
1998	18.972012566318615
1999	19.957720891824938
2000	18.82291277134432
2001	20.366832853926766
2002	19.667053100982034
2003	23.538910069522316
2004	23.89107207556444
2005	24.114525404585155
2006	31.689231091159996
2007	33.948858857817555
2008	32.24355078166275
2009	29.286157273467282
2010	30.357418364222877
2011	33.92911809841211
2012	33.95868642287404
2013	31.05396483912535
2014	32.183524642537584
2015	28.823826581562912
2016	31.05283419356083
2017	29.36726566024038
2018	29.434563679538318
2019	28.826932350928043
2020	29.098076881876572
2021	29.45634050501649