Year	Percent
1991	51.94
1992	52.58
1993	51.95
1994	53.38
1995	56.22
1996	58.99
1997	58.98
1998	60.31
1999	61.32
2000	61.95
2001	61.62
2002	61.32
2003	60.89
2004	62.41
2005	62.63
2006	62.69
2007	63.37
2008	62.62
2009	61.03
2010	60.16
2011	59.74
2012	58.51
2013	59.17
2014	56.95
2015	57.93
2016	59.63
2017	59.33
2018	59
2019	58.7
2020	53.76