Year	Percent
1990	55.4
1991	56.06
1992	56.66
1993	57.21
1994	57.71
1995	58.14
1996	58.22
1997	58.35
1998	58.47
1999	58.64
2000	58.81
2001	59.33
2002	59.85
2003	60.37
2004	60.85
2005	61.59
2006	61.91
2007	62.22
2008	62.33
2009	62.34
2010	62.26
2011	62.08
2012	61.78
2013	61.37
2014	60.95
2015	60.61
2016	60.46
2017	60.34
2018	60.3
2019	60.37