Year	Percent
1971	6.84
1972	6.457
1973	7.027
1974	7.306
1975	8.339
1976	7.973
1977	8.051
1978	8.21
1979	7.985
1980	7.564
1981	8.575
1982	9.116
1983	8.704
1984	18.23
1985	14.25
1986	13.85
1987	12.87
1988	11.14
1989	10.13
1990	22.11
1991	33.09
1992	20.44
1993	16.74
1994	16.98
1995	16.62
1996	18.01
1997	18.46
1998	16.17
1999	16.7
2000	15.63
2001	16.52
2002	17.27
2003	14.64
2004	15.36
2005	14.86
2006	16.54
2007	17.65
2008	18.11
2009	17.97
2010	16.98