Year	Percent
1986	66.8
1990	61.5
1991	61.2
1992	60.6
1993	56.1
1994	58
1995	55.2
1996	54
1997	52.5
1998	50.7
1999	49.5
2000	42.3
2001	43.2
2002	41
2003	38.9
2004	42.7
2005	37.3
2006	37.9
2007	41.3
2011	36.8
2012	31.9
2013	35.1
2014	32.6