Year	Percent
1971	12.34
1972	11.64
1973	11.28
1974	13.33
1975	12.47
1976	11.82
1977	10.97
1978	10.44
1979	10.03
1980	10.55
1981	10.94
1982	11.51
1983	11.54
1984	11.31
1985	11.62
1986	10.7
1987	10.55
1988	10.63
1989	10.74
1990	12
1991	10.66
1992	12
1993	11.5
1994	11.19
1995	11.05
1996	10.98
1997	11.21
1998	11.47
1999	11.22
2000	12.05
2001	11.89
2002	12.88
2003	13.4
2004	12.6
2005	19.81
2006	17.87
2007	17.84
2008	16.86
2009	18.04
2010	17.14