Year	Percent
1960	3.57474
1961	3.60096
1962	3.60088
1963	3.56042
1964	3.47744
1965	3.36365
1966	3.25327
1967	3.14834
1968	3.03134
1969	2.90228
1970	2.77246
1971	2.64179
1972	2.5324
1973	2.4702
1974	2.4665
1975	2.50205
1976	2.54621
1977	2.57987
1978	2.61215
1979	2.63686
1980	2.65519
1981	2.67673
1982	2.69504
1983	2.69086
1984	2.66129
1985	2.61432
1986	2.55845
1987	2.51106
1988	2.48763
1989	2.49524
1990	2.51986
1991	2.54027
1992	2.54376
1993	2.53218
1994	2.50316
1995	2.45769
1996	2.41458
1997	2.36273
1998	2.2725
1999	2.13635
2000	1.97378
2001	1.80143
2002	1.64783
2003	1.53296
2004	1.46922
2005	1.44173
2006	1.42472
2007	1.39834
2008	1.3647
2009	1.31773
2010	1.26236
2011	1.207
2012	1.15939
2013	1.11702
2014	1.08146
2015	1.05123
2016	1.0227
2017	0.99345