Year	Percent
1960	5.88433
1961	3.75813
1962	1.74106
1963	1.85386
1964	2.14701
1965	2.49987
1966	2.99754
1967	3.30317
1968	3.00066
1969	1.94183
1970	0.43061
1971	-1.25699
1972	-2.72097
1973	-3.69743
1974	-3.87744
1975	-3.32487
1976	-2.61692
1977	-1.87743
1978	-0.5554
1979	1.38639
1980	3.61699
1981	5.94502
1982	7.66687
1983	8.22129
1984	10.30761
1985	9.06585
1986	7.72433
1987	6.71212
1988	6.04896
1989	5.8248
1990	5.91356
1991	6.02232
1992	6.05133
1993	6.09297
1994	6.16411
1995	7.76858
1996	7.81453
1997	7.82724
1998	7.81705
1999	7.75429
2000	7.66299
2001	7.54074
2002	7.448
2003	7.39012
2004	7.38567
2005	7.38717
2006	7.39178
2007	7.34765
2008	7.26255
2009	7.11767
2010	6.94397
2011	6.76094
2012	6.57504
2013	5.04096
2014	4.9005
2015	4.74685
2016	4.58373
2017	4.42388