Year	Percent
1990	57.97
1991	57.72
1992	57.47
1993	57.22
1994	56.97
1995	56.72
1996	56.47
1997	56.22
1998	55.97
1999	55.72
2000	55.47
2001	55.22
2002	54.97
2003	54.72
2004	54.47
2005	54.22
2006	53.75
2007	53.29
2008	52.82
2009	52.35
2010	51.89
2011	51.62
2012	51.35
2013	51.09
2014	50.82
2015	50.55