Year	Percent
1990	60.88
1991	60.74
1992	60.6
1993	60.46
1994	60.32
1995	60.18
1996	60.04
1997	59.91
1998	59.77
1999	59.63
2000	59.49
2001	59.39
2002	59.3
2003	59.2
2004	59.1
2005	59.01
2006	58.89
2007	58.78
2008	58.67
2009	58.56
2010	58.45
2011	58.32
2012	58.18
2013	58.05
2014	57.92
2015	57.79