Year	Percent
1991	61.94
1992	62.26
1993	62.16
1994	62.11
1995	62.19
1996	62.13
1997	62.15
1998	62.02
1999	61.98
2000	61.89
2001	62.03
2002	61.69
2003	61.59
2004	63.06
2005	62.25
2006	61.47
2007	60.7
2008	59.91
2009	58.98
2010	58.16
2011	57.37
2012	56.58
2013	55.79
2014	55.05
2015	55.49
2016	55.44
2017	55.43
2018	55.43
2019	55.37
2020	54.48