Year	Percent
1990	58.98
1991	58.66
1992	58.33
1993	58.01
1994	57.68
1995	57.35
1996	57.03
1997	56.7
1998	56.38
1999	56.05
2000	55.72
2001	55.4
2002	55.07
2003	54.75
2004	54.42
2005	54.09
2006	54.05
2007	54
2008	53.95
2009	53.9
2010	53.86
2011	53.67
2012	53.48
2013	53.3
2014	53.11
2015	52.93