Year	Percent
1990	52.16
1991	52.31
1992	52.46
1993	52.61
1994	52.76
1995	52.91
1996	53.06
1997	53.21
1998	53.36
1999	53.51
2000	53.66
2001	53.85
2002	54.03
2003	54.22
2004	54.4
2005	54.58
2006	54.54
2007	54.49
2008	54.44
2009	54.39
2010	54.35
2011	54.61
2012	54.88
2013	55.14
2014	55.41
2015	55.68