Year	Percent
1991	52.78
1992	54.06
1993	53.85
1994	53.97
1995	54.25
1996	55.19
1997	56.93
1998	58.32
1999	59.54
2000	61.13
2001	62.12
2002	62.45
2003	61.78
2004	61.29
2005	59.23
2006	59.95
2007	61.49
2008	62.56
2009	62.24
2010	61.22
2011	60.94
2012	60.83
2013	59.83
2014	59.27
2015	59.67
2016	59.89
2017	60.51
2018	61.39
2019	62.08
2020	61.24