Year	Percent
1991	56.67
1992	56.25
1993	56.73
1994	58.36
1995	60.09
1996	60.95
1997	60.42
1998	59.48
1999	60.02
2000	60.73
2001	61.81
2002	62.58
2003	62.67
2004	63.71
2005	64.62
2006	65.11
2007	65.49
2008	65.03
2009	63.35
2010	62.8
2011	63.14
2012	62.66
2013	63.67
2014	64.73
2015	64.68
2016	65.81
2017	66.8
2018	67
2019	66.77
2020	66.37