Year	Percent
1980	46.6
1986	48.4
1987	50.5
1991	52.4
1992	50.9
1993	49.9
1994	51
1995	53.8
1996	54
1997	53.7
1998	55.1
1999	54.2
2000	55.1
2001	57
2002	57.8
2003	54.5
2004	52.3
2005	51.7
2006	50.7
2007	50.5
2008	48.8
2009	48.2
2010	48
2011	47.4
2012	46.3
2013	46
2014	46.6
2016	47.6