Year	Percent
1977	6.2
1978	5.8
1979	5.8
1980	7.1
1981	12
1982	15.3
1983	7.7
1984	12.2
1985	13.5
1986	12
1987	11
1988	10.6
1989	12.2
1990	24.89
1991	9.65
1995	23
1996	22.4
1997	25.6
1998	26.5
1999	26.6
2000	25.8
2001	26.3
2002	23.36
2003	24.5
2004	26.3
2005	26.5
2006	29.1
2008	21.76
2009	20.47
2010	20.97
2011	21.03
2012	22.27
2013	21.28
2016	23.2