Year	Percent
1991	69.98
1992	70.13
1993	70.14
1994	70.12
1995	70.27
1996	70.36
1997	70.45
1998	70.54
1999	70.58
2000	71.06
2001	71.56
2002	72.05
2003	72.57
2004	73.06
2005	73.51
2006	73.49
2007	73.41
2008	73.28
2009	72.96
2010	72.8
2011	72.71
2012	72.64
2013	72.57
2014	71.68
2015	70.77
2016	70.06
2017	69.35
2018	68.62
2019	67.92