Year	Percent
1991	66.58
1992	66.54
1993	66.57
1994	66.25
1995	66.33
1996	66.25
1997	66.04
1998	65.86
1999	65.88
2000	65.71
2001	66.06
2002	66.48
2003	66.47
2004	66.51
2005	66.49
2006	66.32
2007	66.35
2008	66.35
2009	66.32
2010	68.43
2011	68.42
2012	68.38
2013	68.4
2014	68.48
2015	68.7
2016	68.73
2017	68.71
2018	68.74
2019	68.73
2020	67.17