Year	% of revenue
1975	7.203579418344519
1976	7.920792079207921
1977	7.361405634656165
1978	8.020116463737427
1979	9.12216364886546
1981	6.575446598251615
1982	5.879771829749891
1983	5.292141123763301
1984	5.597857919839344
1985	5.911664779161948
1986	6.59261206783226
1987	7.685352622061482
1988	6.88113469345804
1989	7.378736352246286
1990	9.712000680648318
1991	8.702315601749937
1992	8.610398933442724
1993	8.805623877056187
1994	9.341107698698831
1995	9.217341262229043
1996	10.629781703246389
1997	10.687250148847495
2002	2.716231826743956
2003	2.952317188374162
2004	3.0638174293942546
2005	3.535989576045367
2006	2.745517545574841
2007	2.686348858717481
2008	2.344921330401063
2009	1.9688464105722305
2010	1.866967021607624
2011	1.7321366782723002
2012	1.7794849010362175
2013	2.417023216404839
2014	2.8832524458824436
2015	2.547090432576308