Year	Percent
1990	59.4
1991	59.18
1992	58.85
1993	58.45
1994	58.04
1995	57.66
1996	57.45
1997	57.3
1998	57.22
1999	57.24
2000	57.33
2001	57.49
2002	57.69
2003	57.89
2004	58.15
2005	58.43
2006	58.99
2007	59.59
2008	60.1
2009	60.59
2010	60.92
2011	61.07
2012	61.16
2013	61.16
2014	61.05
2015	60.9
2016	60.73
2017	60.48
2018	60.19
2019	59.89