Year	Percent
1991	71.12
1992	71.05
1993	70.94
1994	70.81
1995	70.65
1996	70.48
1997	70.3
1998	70.4
1999	70.2
2000	70.02
2001	69.92
2002	69.83
2003	69.74
2004	69.67
2005	69.6
2006	69.62
2007	69.64
2008	69.64
2009	69.5
2010	69.48
2011	69.52
2012	69.63
2013	69.69
2014	69.81
2015	69.86
2016	69.93
2017	69.99
2018	70.05
2019	70.06
2020	67.15