Year	Percent
1990	98.91
1991	98.89
1992	98.86
1993	98.84
1994	98.81
1995	98.79
1996	98.76
1997	98.74
1998	98.71
1999	98.69
2000	98.66
2001	98.63
2002	98.61
2003	98.58
2004	98.56
2005	98.53
2006	98.51
2007	98.48
2008	98.46
2009	98.43
2010	98.4
2011	98.38
2012	98.36
2013	98.33
2014	98.31
2015	98.28