Year	Percent
1990	65.82
1991	65.95
1992	66.12
1993	66.32
1994	66.52
1995	66.7
1996	66.77
1997	66.84
1998	66.93
1999	67.05
2000	67.23
2001	67.43
2002	67.66
2003	67.91
2004	68.15
2005	68.37
2006	68.49
2007	68.58
2008	68.65
2009	68.69
2010	68.71
2011	68.63
2012	68.53
2013	68.41
2014	68.28
2015	68.15
2016	68.1
2017	68.08
2018	68.08
2019	68.08