Year	Percent
1960	6.61739
1961	6.73525
1962	6.8536
1963	6.97334
1964	7.09681
1965	7.2236
1966	7.35597
1967	7.49276
1968	7.63255
1969	7.79062
1970	8.04826
1971	8.30826
1972	8.57254
1973	8.76613
1974	8.73113
1975	8.70482
1976	8.68981
1977	8.68135
1978	8.67099
1979	8.64675
1980	8.60291
1981	8.53913
1982	8.4632
1983	8.60516
1984	8.78873
1985	8.98542
1986	9.19888
1987	9.42946
1988	9.68397
1989	9.96702
1990	10.28631
1991	10.6449
1992	11.04446
1993	11.08323
1994	11.07961
1995	11.08761
1996	11.10477
1997	11.13055
1998	11.1676
1999	11.21859
2000	11.28488
2001	11.36553
2002	11.45735
2003	11.39801
2004	11.30819
2005	11.20398
2006	11.08418
2007	10.9502
2008	10.80219
2009	10.6409
2010	10.46801
2011	10.28425
2012	10.09179
2013	9.8948
2014	9.69823
2015	9.50548
2016	9.31746
2017	9.13436