Year	% of revenue
1972	25.27075812274368
1973	34
1974	38.72387238723872
1975	48.182419035029746
1976	43.66045845272206
1977	42.68292682926829
1978	42.24250325945241
1979	41.55511485704842
1980	43.33885586200175
1981	43.90478811227298
1982	43.18530421444745
1983	39.23908430486557
1984	43.40689107194453
1985	44.71615560304895
1986	43.61115537848605
1987	41.371658974489016
1988	43.23401269569025
1989	43.64496527777778
1990	36.36714230620902
1991	35.995128740431454
1992	36.581377452866484
1993	30.265307272010368
1994	29.89862940886138
1995	33.01275412067588
1996	33.63656436299404
1997	41.07564319311695
1998	40.19520095469463
1999	43.17114810072557
2000	35.13703855860086
2001	45.463132509691576
2002	45.7483688859702
2003	49.08917569137805
2004	50.80522658624997
2005	50.65148234278385
2006	50.615416701128666
2007	51.062659605259434
2008	47.76191741688819
2009	40.54527492965632
2010	39.8992255260249
2011	36.54752144542839
2012	36.086767630372634
2013	33.772924939080525
2014	33.46051169210965
2015	33.10560141123711
2016	27.235320145213326
2017	30.472616826986453
2018	28.231332934068952
2019	28.1445611613427
2020	29.270191201799584