Year	Percent
1990	17.44
1991	17.55
1992	17.66
1993	17.78
1994	17.89
1995	18
1996	18.12
1997	18.23
1998	18.35
1999	18.46
2000	18.57
2001	18.6
2002	18.63
2003	18.65
2004	18.68
2005	18.71
2006	18.71
2007	18.71
2008	18.71
2009	18.71
2010	18.71
2011	18.7
2012	18.7
2013	18.7
2014	18.69
2015	18.69