Year	Percent
1960	2.50092
1961	2.49014
1962	2.49698
1963	2.55417
1964	2.68279
1965	2.84561
1966	3.0116
1967	3.14476
1968	3.23329
1969	3.25884
1970	3.24587
1971	3.21688
1972	3.1921
1973	3.17715
1974	3.18676
1975	3.20498
1976	3.22558
1977	3.23091
1978	3.17936
1979	3.06779
1980	2.92174
1981	2.70235
1982	2.5065
1983	2.47396
1984	2.65166
1985	2.92301
1986	3.32069
1987	3.55644
1988	3.30891
1989	2.4791
1990	1.31576
1991	0.00074
1992	-1.07766
1993	-1.59451
1994	-1.27241
1995	-0.31531
1996	0.85191
1997	1.80762
1998	2.50286
1999	2.79877
2000	2.80718
2001	2.78329
2002	2.80938
2003	2.77047
2004	2.66658
2005	2.52257
2006	2.34632
2007	2.16756
2008	2.01634
2009	1.90877
2010	1.82836
2011	1.75313
2012	1.66823
2013	1.58034
2014	1.49048
2015	1.39889
2016	1.30955
2017	1.22652