Year	Percent
1960	6.02245
1961	5.8193
1962	5.48205
1963	5.412
1964	5.29426
1965	5.13398
1966	4.9859
1967	4.84438
1968	4.69965
1969	4.54111
1970	4.39278
1971	4.23736
1972	3.98698
1973	3.82725
1974	3.77435
1975	3.74353
1976	3.72346
1977	3.69133
1978	3.65499
1979	3.60575
1980	3.54979
1981	3.48574
1982	3.3567
1983	3.28171
1984	3.25048
1985	3.22132
1986	3.19615
1987	3.16107
1988	3.10993
1989	3.03617
1990	2.94995
1991	2.78922
1992	2.68106
1993	2.60722
1994	2.54422
1995	2.48764
1996	2.43193
1997	2.37391
1998	2.32382
1999	2.27753
2000	2.23464
2001	2.19336
2002	1.85748
2003	1.82311
2004	1.78724
2005	1.75028
2006	1.71408
2007	1.67819
2008	1.63942
2009	1.60062
2010	1.55939
2011	1.51669
2012	1.46522
2013	1.4223
2014	1.39002
2015	1.35805
2016	1.32953
2017	1.30734