Year	Percent
1971	2.932
1972	2.889
1973	13.43
1974	19.89
1975	15.84
1976	11.25
1977	15.95
1978	17.08
1979	16.3
1980	14.74
1981	3.927
1982	3.434
1983	14.12
1984	13.69
1985	11.16
1986	10.65
1987	11.18
1988	9.979
1989	11.99
1990	10.66
1991	8.422
1992	8.575
1993	10.37
1994	10.65
1995	13.14
1996	15.41
1997	19
1998	20.72
1999	20.65
2000	18.3
2001	16.07
2002	12.75
2003	14.15
2004	11.53
2005	13.2
2006	12.57
2007	13.9