Year	Percent
1990	82.4
1991	82.58
1992	82.66
1993	82.64
1994	82.5
1995	82.4
1996	82.15
1997	81.84
1998	81.48
1999	81.07
2000	80.67
2001	79.77
2002	78.91
2003	78.17
2004	77.55
2005	77.13
2006	77.49
2007	77.9
2008	78.44
2009	78.93
2010	79.42
2011	80.06
2012	80.64
2013	81.18
2014	81.32
2015	81.66
2016	81.59
2017	81.63
2018	81.46
2019	81.25