Year	Percent
1990	66.31
1991	65.89
1992	65.48
1993	65.06
1994	64.64
1995	64.22
1996	63.81
1997	63.39
1998	62.97
1999	62.56
2000	62.14
2001	61.73
2002	61.31
2003	60.9
2004	60.48
2005	60.07
2006	59.65
2007	59.23
2008	58.81
2009	58.39
2010	57.97
2011	57.55
2012	57.14
2013	56.73
2014	56.31
2015	55.9