Year	% of revenue
1972	12.63537906137184
1973	10.545454545454545
1974	5.83058305830583
1975	4.49438202247191
1976	2.722063037249284
1977	3.7694013303769403
1978	4.8674489352455454
1979	4.949595108246571
1980	5.535522853523048
1981	6.735002751788663
1982	8.775838141845007
1983	9.82849439548643
1984	7.147500722334585
1985	4.358793260014126
1986	4.713944223107569
1987	6.45940051732008
1988	6.195520826149404
1989	5.121527777777778
1990	5.090628615503278
1991	4.140570633263744
1992	5.194305502116198
1993	5.858164817213992
1994	6.796005922776112
1995	7.519308732577752
1996	6.654890704349746
1997	7.411995112234479
1998	7.146002926593644
1999	10.016157551368819
2000	11.522096367157697
2001	12.608434682548571
2002	13.764823852893098
2003	11.462453126981195
2004	11.565932924340586
2005	11.575113202321448
2006	10.025667008420776
2007	9.760457788666656
2008	9.189395833327312
2009	6.26873280895308
2010	7.161625199871086
2011	6.007064247226645
2012	4.916465490287229
2013	6.399063894180776
2014	5.8774332270982725
2015	5.1944398701553585
2016	5.240605380697219
2017	5.974170667889756
2018	8.536516010554559
2019	9.30427433647019
2020	8.039085285281148