Year	Percent
1991	62.58
1992	62.79
1993	62.44
1994	61.97
1995	61.58
1996	61.53
1997	61.71
1998	60.95
1999	60.08
2000	59.65
2001	59.13
2002	58.23
2003	57.93
2004	57.86
2005	57.94
2006	58.05
2007	58.34
2008	58.16
2009	57.29
2010	57.01
2011	56.9
2012	56.73
2013	57.23
2014	57.67
2015	57.95
2016	58.57
2017	59.17
2018	60.4
2019	60.87
2020	60.49