Year	Percent
1960	6.62073
1961	6.73328
1962	6.84859
1963	6.96862
1964	7.0967
1965	7.23417
1966	7.38323
1967	7.54309
1968	7.71236
1969	7.88728
1970	8.04349
1971	8.17432
1972	8.30791
1973	8.44478
1974	8.58782
1975	8.73832
1976	8.8972
1977	9.06323
1978	9.2367
1979	9.36885
1980	9.44815
1981	9.52166
1982	9.61341
1983	9.70316
1984	9.7924
1985	9.88775
1986	9.98128
1987	10.07296
1988	10.15978
1989	10.16893
1990	10.1205
1991	10.07453
1992	10.02097
1993	9.99107
1994	10.01644
1995	10.07162
1996	10.13704
1997	10.20551
1998	10.27276
1999	10.34568
2000	10.42586
2001	10.50676
2002	10.60945
2003	10.7109
2004	10.80792
2005	10.92063
2006	11.04644
2007	11.16516
2008	11.27929
2009	11.37567
2010	11.45966
2011	11.54007
2012	11.60823
2013	11.6746
2014	11.7712
2015	11.84285
2016	11.92358
2017	12.01152