Year	% of revenue
1975	3.713646532438479
1976	4.125412541254125
1977	5.119660708876098
1978	7.834833245103229
1979	10.589044235617694
1981	5.903965539085265
1982	5.660377358490567
1983	8.390890423744633
1984	9.438540707890553
1985	9.603624009060024
1986	10.299723938477717
1987	11.36829415310428
1988	12.477516830258493
1989	13.822265974583855
1990	15.995235461777343
1991	16.384763284754925
1992	18.02481796738796
1993	23.432239607863657
1994	24.70438124063441
1995	20.45709901071497
1996	23.67884677871976
1997	21.90893368489694
2002	21.129369646889863
2003	21.76130162427889
2004	22.197752555197923
2005	22.42323843742994
2006	19.787199938157364
2007	18.656183717748107
2008	16.459298193779638
2009	15.164068223768526
2010	20.502389127098397
2011	25.28465258428157
2012	26.772820431972256
2013	33.527897591152446
2014	30.685232262537554
2015	33.25445457567996