Year	Percent
1991	81.2
1992	81.2
1993	81.2
1994	80.6
1995	80.7
1996	80.7
1997	80.7
1998	78.2
1999	78.2
2000	78.2
2001	78.3
2002	78.2
2003	78
2004	78
2005	78.21
2006	78.21
2007	78.2
2008	78.2
2009	78.22