Year	Percent
1991	84.55
1992	84.54
1993	84.54
1994	84.58
1995	84.64
1996	84.59
1997	84.55
1998	84.51
1999	84.46
2000	84.25
2001	84.07
2002	83.86
2003	83.64
2004	83.43
2005	83.19
2006	82.99
2007	82.78
2008	82.51
2009	82.07
2010	81.66
2011	81.22
2012	80.77
2013	80.32
2014	79.91
2015	79.49
2016	79.6
2017	79.76
2018	79.94
2019	80.11
2020	73.8