Year	Percent
1990	55.16
1991	54.88
1992	54.6
1993	54.33
1994	54.05
1995	53.77
1996	53.49
1997	53.21
1998	52.93
1999	52.66
2000	52.38
2001	52.09
2002	51.81
2003	51.53
2004	51.25
2005	50.97
2006	50.68
2007	50.4
2008	50.12
2009	49.84
2010	49.56
2011	49.3
2012	49.03
2013	48.77
2014	48.51
2015	48.25