Year	Percent
1991	69.09
1992	68.76
1993	67.41
1994	65.68
1995	65.23
1996	64.66
1997	63.34
1998	64.39
1999	59.78
2000	58.49
2001	59.66
2002	60.61
2003	61.67
2004	62.38
2005	62.48
2006	62.13
2007	61.27
2008	60.56
2009	60.11
2010	60.55
2011	56.99
2012	57.46
2013	57.68
2014	59.99
2015	60.26
2016	61.08
2017	60.87
2018	60.67
2019	60.43
2020	57.81