Year	Percent
1960	1.46849
1961	1.4094
1962	1.39705
1963	1.5148
1964	1.80618
1965	2.16423
1966	2.65798
1967	2.96473
1968	2.66091
1969	1.60639
1970	0.09204
1971	-1.59462
1972	-3.05652
1973	-4.03258
1974	-4.21356
1975	-3.65857
1976	-2.95094
1977	-2.21188
1978	-0.89258
1979	1.05501
1980	3.28332
1981	5.6118
1982	7.3351
1983	7.88983
1984	7.23957
1985	5.97324
1986	4.66203
1987	3.69373
1988	3.06725
1989	2.89365
1990	3.0224
1991	3.17686
1992	3.24307
1993	3.34071
1994	3.45218
1995	3.57514
1996	3.71868
1997	3.86279
1998	3.96647
1999	4.0235
2000	4.05034
2001	4.05754
2002	4.08044
2003	4.14514
2004	4.25672
2005	4.38627
2006	4.50534
2007	4.57792
2008	4.60586
2009	4.5794
2010	4.51562
2011	4.44055
2012	4.35933
2013	4.25566
2014	4.12842
2015	3.98914
2016	3.84723
2017	3.71241