Year	Percent
1981	25
1982	25
1983	25
1984	30
1985	40
1986	60
1987	60
1988	60
1989	60
1990	60
1991	60
1992	60
1993	60
1994	60
1995	60
1996	87
1997	90
1998	78
1999	65
2000	75
2001	79
2002	78
2003	79
2004	74
2005	75
2006	80
2007	79
2008	83
2009	76
2010	76
2011	76