Year	Percent
1990	81.19
1991	81.55
1992	82.02
1993	82.37
1994	82.59
1995	82.76
1996	82.84
1997	82.9
1998	82.79
1999	82.53
2000	82.39
2001	82.18
2002	82.02
2003	81.87
2004	81.72
2005	81.54
2006	81.43
2007	81.33
2008	81.17
2009	81.1
2010	81.04
2011	80.95
2012	80.86
2013	80.8
2014	80.75
2015	80.75
2016	80.68
2017	80.73
2018	80.79
2019	80.68
2020	79.23