Year	Percent
1990	73.33
1991	72.54
1992	71.74
1993	70.95
1994	70.16
1995	69.37
1996	68.58
1997	67.78
1998	66.99
1999	66.2
2000	65.41
2001	64.49
2002	63.56
2003	62.64
2004	61.72
2005	60.79
2006	60.07
2007	59.35
2008	58.63
2009	57.91
2010	57.18
2011	56.46
2012	55.74
2013	55.02
2014	54.3
2015	53.57