Year	Percent
1960	9.799
1961	10.114
1962	10.438
1963	10.772
1964	11.115
1965	11.466
1966	11.828
1967	12.2
1968	12.358
1969	12.517
1970	12.678
1971	12.841
1972	13.006
1973	13.173
1974	13.341
1975	13.511
1976	13.684
1977	13.857
1978	14.033
1979	14.211
1980	14.39
1981	14.572
1982	14.755
1983	14.94
1984	15.182
1985	15.757
1986	16.351
1987	16.962
1988	17.592
1989	18.239
1990	18.905
1991	19.59
1992	20.294
1993	21.015
1994	21.755
1995	22.514
1996	23.293
1997	24.088
1998	24.903
1999	25.735
2000	26.587
2001	27.455
2002	28.341
2003	29.244
2004	30.164
2005	31.099
2006	32.051
2007	33.017
2008	34
2009	34.585
2010	35.175
2011	35.771