Year	Percent
1990	76.45
1991	75.97
1992	75.48
1993	75
1994	74.51
1995	74.03
1996	73.54
1997	73.06
1998	72.57
1999	72.09
2000	71.6
2001	71.9
2002	72.2
2003	72.5
2004	72.79
2005	73.09
2006	73.91
2007	74.73
2008	75.55
2009	76.37
2010	77.19
2011	78.01
2012	78.83
2013	79.65
2014	80.47
2015	81.29