Year	Percent
1990	67.69
1991	67.58
1992	67.43
1993	67.24
1994	67.03
1995	66.74
1996	66.57
1997	66.44
1998	66.29
1999	65.73
2000	65.17
2001	64.59
2002	64.01
2003	63.41
2004	62.8
2005	62.17
2006	61.57
2007	60.96
2008	60.35
2009	59.73
2010	59.11
2011	58.49
2012	57.88
2013	57.27
2014	56.67
2015	56.07
2016	55.49
2017	53.8
2018	53.74
2019	53.69
2020	52.81