Year	Percent
1960	4.5
1961	4.645
1962	4.705
1963	4.649
1964	4.76
1965	4.747
1966	4.867
1967	4.846
1968	4.767
1969	5.036
1970	12.76
1971	13
1972	13.88
1973	12.75
1974	13.33
1975	13.84
1976	13.66
1977	13.69
1978	13.43
1979	13.57
1980	12.91
1981	13.09
1982	13.39
1983	13.89
1984	13.55
1985	13.05
1986	13.53
1987	13.63
1988	13.07
1989	12.74
1990	13.24
1991	13.57
1992	13.71
1993	14.21
1994	13.31
1995	13.37
1996	13.16
1997	13.14
1998	13.19
1999	13.04
2000	13.02
2001	13.15
2002	13.68
2003	13.24
2004	13
2005	12.84
2006	12.86
2007	13.03
2008	12.97
2009	13.44
2010	13.49