Year	Percent
1990	50.22
1991	49.85
1992	49.48
1993	49.11
1994	48.74
1995	48.37
1996	48.01
1997	47.64
1998	47.27
1999	46.9
2000	46.53
2001	46.98
2002	47.43
2003	47.88
2004	48.34
2005	48.79
2006	49.23
2007	49.68
2008	50.13
2009	50.57
2010	51.02
2011	51.61
2012	52.2
2013	52.79
2014	53.38
2015	53.98