Year	Percent
1990	61.16
1991	61.35
1992	61.12
1993	61.06
1994	60.85
1995	60.75
1996	60.53
1997	60.03
1998	59.55
1999	59.09
2000	58.68
2001	58.58
2002	58.54
2003	58.55
2004	58.56
2005	58.56
2006	59.53
2007	60.47
2008	61.37
2009	62.27
2010	63.19
2011	64.22
2012	63.5
2013	62.73
2014	61.89
2015	61.34
2016	60.68
2017	60.5
2018	60.37
2019	60.29