Year	Percent
1991	69.72
1992	69.73
1993	69.66
1994	69.59
1995	69.51
1996	69.52
1997	69.46
1998	69.38
1999	69.28
2000	69.28
2001	69.3
2002	69.27
2003	69.31
2004	69.31
2005	69.36
2006	69.54
2007	69.7
2008	69.8
2009	69.61
2010	69.53
2011	69.66
2012	69.69
2013	69.98
2014	69.92
2015	69.77
2016	69.58
2017	69.39
2018	69.16
2019	68.91
2020	67.46