Year	Percent
1960	8.02298
1961	8.21965
1962	8.32414
1963	8.38097
1964	8.43866
1965	8.49603
1966	8.55466
1967	8.61494
1968	8.67817
1969	8.7441
1970	8.81478
1971	8.89023
1972	9.02364
1973	9.1794
1974	9.34414
1975	9.51797
1976	9.70242
1977	9.89629
1978	10.10121
1979	10.31619
1980	10.542
1981	10.66931
1982	10.74945
1983	10.83692
1984	10.93474
1985	11.04333
1986	11.16488
1987	11.29864
1988	11.44466
1989	11.60059
1990	11.76742
1991	11.80525
1992	11.78474
1993	11.77587
1994	11.78026
1995	11.79828
1996	11.83073
1997	11.87665
1998	11.93621
1999	12.00819
2000	12.09246
2001	12.13831
2002	12.18744
2003	12.2397
2004	12.2949
2005	12.35318
2006	12.41568
2007	12.48232
2008	12.55391
2009	12.63002
2010	12.70872
2011	12.77499
2012	12.84645
2013	12.92313
2014	13.00725
2015	13.09939
2016	13.20007
2017	13.30933