Year	Percent
1960	3.28425
1961	3.3707
1962	3.4601
1963	3.56962
1964	3.70449
1965	3.85102
1966	3.98001
1967	4.08436
1968	4.1716
1969	4.24294
1970	4.29564
1971	4.33938
1972	4.36206
1973	4.34115
1974	4.27362
1975	4.17855
1976	4.05835
1977	3.94836
1978	3.88282
1979	3.87275
1980	3.88691
1981	3.90822
1982	3.8865
1983	3.78431
1984	3.58736
1985	3.33516
1986	3.07102
1987	2.84096
1988	2.65834
1989	2.53825
1990	2.45854
1991	2.39701
1992	2.3211
1993	2.21744
1994	2.07522
1995	1.9135
1996	1.74444
1997	1.60318
1998	1.51724
1999	1.50267
2000	1.53509
2001	1.57122
2002	1.58552
2003	1.58728
2004	1.56896
2005	1.52957
2006	1.52043
2007	1.50068
2008	1.37593
2009	1.11672
2010	0.78253
2011	0.39411
2012	0.07678
2013	-0.03692
2014	0.13126
2015	0.49597
2016	0.93067
2017	1.28457