Year	Percent
1981	2
1982	5
1983	5
1984	10
1985	22
1986	17
1987	25
1988	26
1989	18
1990	19
1991	20
1992	21
1993	22
1994	23
1995	22
1996	21
1997	19
1998	33
1999	36
2000	33
2001	33
2002	40
2003	40
2004	30
2005	35
2006	26
2007	40
2008	31
2009	42
2010	45
2011	41