Year	Percent
1980	8
1981	12
1982	12
1983	12
1984	15
1985	12
1986	10
1987	9
1988	16
1989	17
1990	16
1991	18
1992	15
1993	14
1994	14
1995	16
1996	17
1997	16
1998	20
1999	19
2000	15
2001	13
2002	16
2003	15
2004	13
2005	13
2006	11