Year	Percent
1991	65.76
1992	65.71
1993	65.55
1994	65.36
1995	65.18
1996	65.45
1997	65.59
1998	65.64
1999	65.65
2000	65.73
2001	66.29
2002	66.25
2003	66.14
2004	66.03
2005	65.93
2006	67.57
2007	68.88
2008	69.86
2009	70.52
2010	71.07
2011	71.65
2012	66.31
2013	64.43
2014	61.6
2015	61.51
2016	61.51
2017	61.43
2018	61.28
2019	61.07