Year	Percent
1960	6.57685
1961	6.54361
1962	6.53043
1963	6.53948
1964	6.57331
1965	6.63187
1966	6.7179
1967	6.82976
1968	6.96208
1969	7.10574
1970	7.22961
1971	7.3245
1972	7.4229
1973	7.52621
1974	7.63914
1975	7.7639
1976	7.90168
1977	8.04966
1978	8.20525
1979	8.30089
1980	8.31785
1981	8.33086
1982	8.34217
1983	8.35116
1984	8.35766
1985	8.36224
1986	8.3635
1987	8.36465
1988	8.37788
1989	8.32682
1990	8.34021
1991	8.35208
1992	8.42254
1993	8.54421
1994	8.73646
1995	8.96021
1996	9.16821
1997	9.38718
1998	9.62579
1999	9.89279
2000	10.28579
2001	10.6896
2002	11.10147
2003	11.50276
2004	11.79227
2005	11.96896
2006	12.12892
2007	12.28113
2008	12.42713
2009	12.4662
2010	12.7946
2011	13.13153
2012	13.48349
2013	13.84151
2014	14.20763
2015	14.58767
2016	14.98733
2017	15.4086