Year	Percent
1990	68.11
1991	67.87
1992	67.63
1993	67.39
1994	67.15
1995	66.91
1996	66.67
1997	66.43
1998	66.19
1999	65.95
2000	65.72
2001	65.29
2002	64.86
2003	64.44
2004	64.01
2005	63.58
2006	64.33
2007	65.08
2008	65.84
2009	66.59
2010	67.34
2011	67.38
2012	67.42
2013	67.47
2014	67.51
2015	67.55