Year	Percent
1960	8.77906
1961	8.79219
1962	8.8067
1963	8.82008
1964	8.82967
1965	8.83291
1966	8.83036
1967	8.82313
1968	8.81345
1969	8.80298
1970	8.79429
1971	8.78765
1972	8.78308
1973	8.77367
1974	8.74795
1975	8.72307
1976	8.69989
1977	8.67811
1978	8.65809
1979	8.639
1980	8.62102
1981	8.6036
1982	8.58854
1983	8.57905
1984	8.58073
1985	8.58982
1986	8.60692
1987	8.63162
1988	8.6656
1989	8.70979
1990	8.76575
1991	8.8343
1992	8.91447
1993	9.0012
1994	9.08949
1995	9.17506
1996	9.2568
1997	9.3355
1998	9.41468
1999	9.49807
2000	9.58898
2001	9.68654
2002	9.79093
2003	9.90341
2004	10.02605
2005	10.15892
2006	10.30415
2007	10.46034
2008	10.62339
2009	10.78605
2010	10.94458
2011	11.09686
2012	11.24435
2013	11.38777
2014	11.5312
2015	11.67671
2016	11.82467
2017	11.97471