Year	Percent
1990	58.06
1991	57.82
1992	57.59
1993	57.35
1994	57.12
1995	56.88
1996	56.64
1997	56.41
1998	56.17
1999	55.94
2000	55.7
2001	55.41
2002	55.12
2003	54.84
2004	54.55
2005	54.26
2006	53.98
2007	53.7
2008	53.41
2009	53.13
2010	52.85
2011	52.82
2012	52.8
2013	52.78
2014	52.75
2015	52.73