Year	% of revenue
1975	39.19463087248322
1976	38.82013201320132
1977	24.568312632535598
1978	28.79830598200106
1979	26.037130414852168
1981	36.576713543646264
1982	35.02632733655112
1983	36.69031174164644
1984	39.47786796084009
1985	37.54624386560966
1986	38.38569738398843
1987	40.79566003616637
1988	40.97846754715042
1989	38.732772507606946
1990	31.5480495171651
1991	43.02672276869061
1992	38.19095477386934
1993	39.85556544036841
1994	41.239744217444844
1995	40.93338083363021
1996	40.83242253271497
1997	39.82308412009867
2002	47.130264650480285
2003	48.88153127952088
2004	45.83383751603301
2005	43.005583616576615
2006	44.42182817750656
2007	44.408877798016675
2008	44.865092476302834
2009	43.432419113024466
2010	43.80096013374892
2011	36.40198868574891
2012	40.739254439396326
2013	37.786179165933746
2014	49.91333487404668
2015	43.17070316635678