Year	Percent
1990	58.21
1991	59.26
1992	60.26
1993	61.19
1994	61.93
1995	62.32
1996	60.99
1997	59.55
1998	58.38
1999	57.61
2000	56.94
2001	56.72
2002	56.87
2003	57.21
2004	57.35
2005	57.6
2006	58.03
2007	58.96
2008	60.34
2009	62.07
2010	63.96
2011	65.46
2012	67.18
2013	68.96
2014	70.68
2015	72.27
2016	72.84
2017	72.47
2018	70.86
2019	71.36