Year	Percent
1991	57.35
1992	54.71
1993	53.29
1994	53.74
1995	53.8
1996	52.71
1997	51.52
1998	52.5
1999	54.58
2000	56.24
2001	56.31
2002	57.43
2003	58.09
2004	57.79
2005	57.68
2006	58.55
2007	59.56
2008	59.67
2009	55.51
2010	55.1
2011	55.42
2012	54.31
2013	54.99
2014	55.5
2015	55.79
2016	55.44
2017	56.55
2018	56.36
2019	57.52