Year	Percent
1960	5.5879
1961	5.79629
1962	6.01125
1963	6.14773
1964	6.27365
1965	6.39918
1966	6.52575
1967	6.65267
1968	6.77977
1969	6.90477
1970	6.97339
1971	7.02923
1972	7.08277
1973	7.13319
1974	7.18227
1975	7.23006
1976	7.27764
1977	7.32394
1978	7.36996
1979	7.4148
1980	7.44814
1981	7.47794
1982	7.50852
1983	7.54105
1984	7.57779
1985	7.61873
1986	7.66563
1987	7.71823
1988	7.77757
1989	7.84288
1990	7.93224
1991	8.03187
1992	8.13951
1993	8.25407
1994	8.37753
1995	8.50955
1996	8.65076
1997	8.79902
1998	8.95474
1999	9.11586
2000	9.21211
2001	9.29714
2002	9.38423
2003	9.47229
2004	9.5612
2005	9.64918
2006	9.73763
2007	9.82641
2008	9.91661
2009	10.00752
2010	10.10135
2011	10.1978
2012	10.29717
2013	10.40017
2014	10.50763
2015	10.62018
2016	10.73813
2017	10.86155