Year	Percent
1991	77.16
1992	77.11
1993	76.83
1994	76.6
1995	76.4
1996	76.15
1997	75.86
1998	75.6
1999	75.2
2000	74.82
2001	73.74
2002	72.67
2003	71.56
2004	70.88
2005	70.24
2006	69.77
2007	69.41
2008	68.83
2009	68.37
2010	68.05
2011	67.86
2012	67.58
2013	67.34
2014	67.07
2015	66.76
2016	66.48
2017	66.14
2018	65.76
2019	65.1
2020	63.48