Year	Percent
1990	16.8
1991	17.2
1992	17.5
1993	17.8
1994	18.2
1995	18.6
1996	18.7
1997	18.7
1998	18.7
1999	18.7
2000	18.7
2001	18.7
2008	20.78
2009	20.78