Year	Percent
1960	9.50296
1961	9.51315
1962	9.45199
1963	9.38744
1964	9.3352
1965	9.27931
1966	9.22609
1967	9.20844
1968	9.1926
1969	9.14542
1970	9.13633
1971	9.09652
1972	9.03056
1973	8.9802
1974	8.95515
1975	8.96741
1976	8.98507
1977	8.98502
1978	8.97283
1979	8.94931
1980	8.91167
1981	8.87934
1982	8.85323
1983	8.82457
1984	8.79872
1985	8.79564
1986	8.82251
1987	9.09141
1988	8.98199
1989	9.07517
1990	9.10017
1991	9.10406
1992	9.09901
1993	9.09856
1994	9.07607
1995	9.03983
1996	8.9935
1997	8.93379
1998	8.86754
1999	8.82996
2000	8.83031
2001	8.857
2002	8.87187
2003	8.8817
2004	8.89396
2005	8.92645
2006	8.9985
2007	9.07525
2008	9.14612
2009	9.21844
2010	9.2778
2011	9.49781
2012	9.52909
2013	9.55469
2014	9.56681
2015	9.54049
2016	9.52449
2017	9.5457