Year	Percent
1960	3.11159
1961	3.05159
1962	2.97845
1963	2.88594
1964	2.77248
1965	2.64845
1966	2.52762
1967	2.42036
1968	2.32804
1969	2.25484
1970	2.19954
1971	2.14673
1972	2.10529
1973	2.09918
1974	2.13434
1975	2.19615
1976	2.26061
1977	2.31353
1978	2.35831
1979	2.39042
1980	2.40892
1981	2.42665
1982	2.43323
1983	2.40548
1984	2.33728
1985	2.24245
1986	2.13592
1987	2.0371
1988	1.95564
1989	1.89895
1990	1.85783
1991	1.82308
1992	1.77844
1993	1.71418
1994	1.62421
1995	1.51907
1996	1.4133
1997	1.32149
1998	1.24771
1999	1.19788
2000	1.16737
2001	1.14495
2002	1.12631
2003	1.11723
2004	1.11741
2005	1.12615
2006	1.13464
2007	1.14836
2008	1.18103
2009	1.23625
2010	1.30357
2011	1.37644
2012	1.43513
2013	1.46218
2014	1.4479
2015	1.40405
2016	1.35123
2017	1.30336