Year	Percent
1960	2.4491
1961	2.20057
1962	2.07649
1963	1.97056
1964	1.91344
1965	1.76765
1966	1.66556
1967	1.59282
1968	1.49576
1969	1.46799
1970	1.53115
1971	1.27928
1972	1.08411
1973	0.96806
1974	0.92724
1975	0.99956
1976	0.9638
1977	1.01935
1978	1.07179
1979	1.11715
1980	1.02199
1981	1.18734
1982	1.15882
1983	1.11946
1984	1.06779
1985	1.08769
1986	1.12532
1987	1.09324
1988	1.10702
1989	1.14036
1990	1.41026
1991	1.86738
1992	1.90863
1993	1.83118
1994	1.73098
1995	1.68647
1996	1.65278
1997	1.68198
1998	1.63763
1999	1.61296
2000	1.51201
2001	1.21338
2002	1.14842
2003	1.07836
2004	1.14389
2005	1.13588
2006	1.17797
2007	1.16307
2008	1.15619
2009	1.08529
2010	1.03899
2011	0.95537
2012	0.96688
2013	0.9329
2014	0.97837
2015	0.98627
2016	0.9679
2017	0.95187