Year	Percent
1980	46.72607
1981	48.73865
1982	47.41729
1983	46.89319
1984	47.52753
1985	46.73048
1986	45.77273
1987	47.90591
1988	45.01756
1989	45.40692
1990	44.96093
1991	44.22062
1992	46.34346
1993	47.1056
1994	45.49372
1995	48.00464
1996	45.04309
1997	46.61651
1998	47.28974
1999	49.17969
2000	50.55338
2001	50.70888
2002	50.91064
2003	50.15755
2004	50.6288
2005	52.30942
2006	51.40551
2007	53.51984
2008	51.22734
2009	51.50631
2010	51.03591
2011	52.37008
2012	53.47095
2013	51.58705
2014	51.65498
2015	49.76222
2016	50.10023
2017	49.54601