Year	Percent
1991	55.53
1992	56.54
1993	57.51
1994	58.25
1995	58.64
1996	57.32
1997	55.88
1998	54.7
1999	53.92
2000	53.2
2001	52.93
2002	53.07
2003	53.41
2004	53.51
2005	53.71
2006	54.05
2007	54.84
2008	56.09
2009	57.88
2010	59.74
2011	61.27
2012	63.04
2013	64.85
2014	66.55
2015	68.09
2016	68.65
2017	68.82
2018	67.75
2019	68.16
2020	64.3