Year	Percent
1975	25.17509
1976	28.84097
1977	30.98557
1978	33.12932
1979	33.21689
1980	33.64461
1981	32.40867
1982	30.86155
1983	30.08709
1984	29.02647
1985	28.49143
1986	27.59073
1987	27.49691
1988	27.50138
1989	26.57627
1990	25.92636
1991	26.73945
1992	25.55996
1993	24.68012
1994	23.22568
1995	20.05898
1996	20.14195
1997	19.65487
1998	19.23627
1999	18.48856
2000	17.68615
2001	17.39393
2002	17.93015
2003	18.0128
2004	18.06728
2005	17.89124
2006	17.8304
2007	18.19737
2008	17.90014
2009	15.95577
2010	14.71955
2011	12.70482
2012	11.37319
2013	10.00634
2014	9.38208
2015	9.75031
2016	9.91926