Year	Percent
1991	72.14
1992	73.59
1993	73.95
1994	74.49
1995	74.65
1996	73.74
1997	72.42
1998	70.89
1999	69.57
2000	68.05
2001	66.96
2002	65.89
2003	64.88
2004	64.03
2005	63.44
2006	62.54
2007	61.99
2008	61.33
2009	61.05
2010	60.93
2011	60.67
2012	60.94
2013	61.34
2014	61.86
2015	62.27
2016	62.95
2017	63.26
2018	63.56
2019	63.28
2020	59.17