Year	Percent
1990	60.12
1991	60.04
1992	60.01
1993	59.93
1994	59.76
1995	59.5
1996	59.25
1997	59.04
1998	59.65
1999	59.47
2000	59.18
2001	59
2002	58.86
2003	58.67
2004	58.42
2005	58.14
2006	58.01
2007	57.84
2008	57.68
2009	57.5
2010	57.29
2011	57.13
2012	57.14
2013	57.04
2014	56.97
2015	56.79
2016	56.68
2017	56.56
2018	56.46
2019	56.32