Year	Percent
1990	61.83
1991	62.04
1992	62.19
1993	62.27
1994	62.28
1995	62.2
1996	61.99
1997	61.72
1998	61.43
1999	61.14
2000	60.88
2001	60.79
2002	60.74
2003	60.74
2004	60.78
2005	60.86
2006	60.98
2007	61.14
2008	60.96
2009	61.95
2010	64.76
2011	66.24
2012	66.58
2013	66.89
2014	66.18
2015	65.46
2016	64.26
2017	64.07
2018	61.6
2019	61.55