Year	Percent
1990	81.92
1991	81.89
1992	81.87
1993	81.86
1994	81.86
1995	81.83
1996	81.81
1997	81.8
1998	81.79
1999	81.79
2000	81.8
2001	81.79
2002	81.81
2003	81.83
2004	81.86
2005	81.89
2006	81.91
2007	81.93
2008	81.96
2009	81.98
2010	82
2011	82
2012	82
2013	81.99
2014	81.99
2015	81.99
2016	81.99
2017	81.99
2018	81.99
2019	81.99