Year	Percent
1990	68.16
1991	68.04
1992	67.88
1993	67.69
1994	67.47
1995	67.19
1996	67.02
1997	66.89
1998	66.74
1999	66.2
2000	65.66
2001	65.11
2002	64.55
2003	63.98
2004	63.39
2005	62.79
2006	62.21
2007	61.62
2008	61.03
2009	60.43
2010	59.82
2011	59.22
2012	58.62
2013	58.03
2014	57.44
2015	56.87
2016	56.31
2017	54.65
2018	54.59
2019	54.56