Year	Percent
1991	71.7
1992	71.66
1993	71.81
1994	71.72
1995	71.69
1996	71.72
1997	71.7
1998	71.65
1999	71.64
2000	71.64
2001	71.59
2002	71.52
2003	71.4
2004	71.13
2005	70.95
2006	70.98
2007	70.94
2008	70.85
2009	70.62
2010	70.37
2011	70.3
2012	70.12
2013	69.94
2014	69.77
2015	69.62
2016	69.58
2017	69.52
2018	69.4
2019	69.24
2020	66.54