Year	Percent
1991	58.26
1992	57.65
1993	56.88
1994	56.27
1995	56.13
1996	55.8
1997	55.52
1998	55.34
1999	55.07
2000	54.6
2001	54.87
2002	54.99
2003	54.99
2004	55.01
2005	55.15
2006	55.41
2007	55.62
2008	55.76
2009	55.64
2010	55.42
2011	55.45
2012	55.33
2013	55.08
2014	54.75
2015	54.32
2016	56.04
2017	55.45
2018	54.81
2019	54.13