Year	Percent
1990	82.11
1991	82.12
1992	82.11
1993	82.08
1994	82
1995	81.9
1996	81.76
1997	81.58
1998	81.4
1999	81.24
2000	81.08
2001	81
2002	80.94
2003	80.91
2004	80.79
2005	80.71
2006	80.75
2007	80.71
2008	80.65
2009	80.62
2010	80.56
2011	80.53
2012	80.47
2013	80.43
2014	80.39
2015	80.38
2016	80.38
2017	80.39
2018	80.42
2019	80.42