Year	Percent
1991	51.22
1992	51.18
1993	53.12
1994	55.5
1995	56.4
1996	55.96
1997	54.75
1998	53.87
1999	53.92
2000	54.41
2001	53.96
2002	52.66
2003	52.57
2004	53.31
2005	54.71
2006	55.49
2007	56.82
2008	57.92
2009	56.77
2010	57.69
2011	58.38
2012	59.2
2013	59.77
2014	60.38
2015	60.76
2016	61.15
2017	61.4
2018	61.52
2019	61.28
2020	59.31