Year	Percent
1991	57.7
1992	58.96
1993	59.13
1994	58.74
1995	57.26
1996	55.82
1997	56.38
1998	55.41
1999	54.31
2000	54.76
2001	55.19
2002	55.77
2003	56.17
2004	56.48
2005	56.31
2006	56.32
2007	56.31
2008	56.11
2009	56.27
2010	56.42
2011	56.08
2012	55.99
2013	55.99
2014	55.99
2015	56.04
2016	56.01
2017	55.94
2018	55.83
2019	55.7
2020	54.08