Year	% of revenue
1972	4.259789875835719
1973	4.460288509368268
1974	3.9921465968586345
1975	4.444777012870398
1976	5.247776365946637
1977	6.165667166416753
1978	6.716088606477823
1979	8.193000439302974
1980	8.460519495478897
1981	10.318866253321536
1982	11.72132122605972
1983	14.532668190951291
1984	15.24399104833318
1985	14.933565895449652
1986	14.716228893058164
1987	15.734167046614065
1988	15.58347021054204
1989	15.472575441260156
1990	16.064890441052203
1991	17.874842966991995
1992	16.392748899182223
1993	16.41601355644997
1994	16.215058650770025
1995	6.180742572071873
1996	7.4920662149412465
1997	7.894956579826321
1998	9.61222355050807
1999	9.531024276804905
2000	9.880780346820812
2001	9.562109025915998
2002	9.004178822045258
2003	9.158295808798062
2004	8.464182651502291
2005	8.237569266242701
2006	7.709823780311656
2007	6.779782359679268
2008	6.552589362839867
2009	6.026097626672254
2010	4.976114649681529
2011	5.602252787683251
2012	9.0637536436838
2013	8.812641497889004
2014	8.276951161207133
2015	8.114078388784678
2016	7.146683651642098
2017	6.597137514570457
2018	6.1976572904649325
2019	5.763486022265748
2020	5.525905201574535
2021	4.482614639875799
2022	3.6300063158854283