Year	Percent
1990	81.4
1991	81.22
1992	80.79
1993	80.87
1994	80.92
1995	80.92
1996	80.41
1997	79.18
1998	78.53
1999	78.21
2000	77.87
2001	77.79
2002	77.89
2003	78.57
2004	79.32
2005	80.93
2006	81.37
2007	82.93
2008	84.56
2009	86.22
2010	87.85
2011	87.27
2012	87.03
2013	87.2
2014	87.76
2015	88.51
2016	87.96
2017	87.55
2018	87.5
2019	87.67