Year	% of revenue
1972	6.928795175089999
1973	6.427810117241944
1974	8.284705712844897
1975	8.418201145286835
1976	9.226515784736064
1977	9.005951900029626
1978	8.229109153323572
1979	9.633252834513527
1980	11.233238074302045
1981	12.264961940636772
1982	14.684434741741331
1983	16.37482397599951
1984	17.204031629357388
1985	19.22926274559353
1986	18.79548519566987
1987	17.172627552702732
1988	17.47717049149672
1989	17.275810998041184
1990	24.397835410562905
1991	23.80358910690688
1992	22.756135863838942
1993	21.870412878083187
1994	21.382365981944844
1995	22.5372515749689
1996	21.65977991104539
1997	19.301315446186308
1998	18.386070417385724
1999	16.892839377164265
2000	15.458064220123607
2001	17.12714967922767
2002	15.938194201534579
2003	14.98723060143486
2004	14.17782415032745
2005	13.501675866587401
2006	13.07493347891809
2007	12.944792159900912
2008	12.650186742303653
2009	12.790581333654583
2010	12.734459532434343
2011	12.990990141656194
2012	12.14484621900649
2013	10.796433427005752
2014	10.32123277354064
2015	9.51757650559004
2016	9.620046920446358
2017	9.188155336804563
2018	10.452988072237604
2019	10.793089364287363
2020	9.630137204688571
2021	9.109329391895166
2022	10.272799129169941