Year	Percent
1991	80.26
1992	79.82
1993	79.94
1994	79.98
1995	79.97
1996	79.43
1997	78.07
1998	77.35
1999	77
2000	76.6
2001	76.53
2002	76.63
2003	77.32
2004	78.02
2005	79.63
2006	80.06
2007	81.96
2008	83.8
2009	85.48
2010	87
2011	86.33
2012	86.14
2013	86.44
2014	87.02
2015	87.75
2016	87.17
2017	86.71
2018	86.61
2019	86.71
2020	83.31