Year	Percent
1977	7
1978	8
1979	10
1980	14
1981	15
1982	14
1983	12
1984	12
1985	20
1986	12
1987	12
1988	10
1989	12
1990	12
1991	12
1992	12
1993	12
1994	12
1995	12
1996	12
1997	12
1998	12
1999	12
2000	12
2001	12
2002	12
2003	12
2004	12
2005	12
2006	12