Year	Percent
1990	68.39
1991	68.41
1992	68.44
1993	68.46
1994	68.49
1995	68.51
1996	68.54
1997	68.56
1998	68.58
1999	68.61
2000	68.63
2001	68.66
2002	68.69
2003	68.71
2004	68.74
2005	68.77
2006	68.7
2007	68.63
2008	68.56
2009	68.48
2010	68.41
2011	68.41
2012	68.92
2013	68.92
2014	68.92
2015	68.92