Year	Percent
1991	65.28
1992	65.92
1993	65.57
1994	64.33
1995	64.91
1997	67.16
1998	66.99
1999	67.33
2000	67.67
2001	67.77
2002	68.36
2003	69.38
2004	69.52
2005	70.55
2006	69.98
2007	70.38
2008	70.89
2009	71.83
2010	71.88
2011	72.44
2012	72.65
2013	72.97
2014	72.54
2015	71.48
2016	73.33
2017	73.3