Year	Percent
1991	72.7
1992	72.35
1993	72
1994	71.63
1995	71.28
1996	70.91
1997	70.57
1998	70.2
1999	69.85
2000	69.48
2001	69.13
2002	68.78
2003	68.41
2004	68.07
2005	67.7
2006	67.35
2007	66.98
2008	66.63
2009	66.26
2010	65.91
2011	65.54
2012	65.2
2013	64.85
2014	64.48
2015	64.12