Year	Percent
1960	3.90987
1961	3.88346
1962	3.86588
1963	3.87866
1964	3.92441
1965	3.9849
1966	4.05292
1967	4.10056
1968	4.13096
1969	4.12855
1970	4.11079
1971	4.08245
1972	4.06559
1973	3.63209
1974	2.41367
1975	2.4011
1976	2.39376
1977	2.36437
1978	2.35207
1979	2.34205
1980	2.33694
1981	2.31709
1982	2.30139
1983	2.41337
1984	2.84126
1985	2.74042
1986	2.65439
1987	2.56663
1988	2.45893
1989	2.33713
1990	2.20803
1991	2.06936
1992	1.9438
1993	1.87293
1994	1.86784
1995	1.90668
1996	1.95947
1997	1.98991
1998	1.99854
1999	1.95352
2000	1.88931
2001	1.82353
2002	1.76289
2003	1.69241
2004	1.60663
2005	1.51478
2006	1.41106
2007	1.3259
2008	1.28644
2009	1.30385
2010	1.37068
2011	1.44431
2012	1.5086
2013	1.55194
2014	1.57398
2015	1.61826
2016	1.66216
2017	1.70828