Year	Percent
1991	66.87
1992	67.66
1993	68.36
1994	69.1
1995	69.84
1996	69.37
1997	68.67
1998	67.8
1999	66.82
2000	66.02
2001	63.7
2002	61.47
2003	59.51
2004	57.77
2005	56.27
2006	56.76
2007	57.32
2008	57.89
2009	58.15
2010	58.62
2011	59.71
2012	60.63
2013	61.39
2014	62.03
2015	62.5
2016	62.02
2017	61.68
2018	61.3
2019	60.68