Year	Percent
1960	7.50538
1961	7.59544
1962	7.70621
1963	7.79599
1964	7.81779
1965	7.78208
1966	7.81787
1967	7.7802
1968	7.72492
1969	7.55984
1970	4.58678
1971	3.95224
1972	3.82666
1973	3.74324
1974	3.76521
1975	3.84725
1976	3.94891
1977	4.03208
1978	4.07566
1979	4.09613
1980	5.39174
1981	6.89303
1982	6.91267
1983	6.93305
1984	7.0265
1985	7.14201
1986	7.25653
1987	7.3336
1988	7.3715
1989	7.32871
1990	7.23985
1991	6.74707
1992	6.2298
1993	6.15069
1994	6.08713
1995	6.02763
1996	5.96219
1997	5.90291
1998	5.90267
1999	5.94774
2000	6.03072
2001	6.10461
2002	6.17134
2003	6.21086
2004	6.22183
2005	6.18462
2006	6.17099
2007	6.14217
2008	6.1224
2009	6.09106
2010	6.06892
2011	6.03817
2012	6.00763
2013	5.95774
2014	5.9225
2015	5.87426
2016	5.8154
2017	5.75732