Year	Percent
1968	23.01843
1969	23.24761
1970	29.23795
1971	36.06725
1972	43.31186
1973	78.78854
1974	49.7339
1975	51.60092
1976	35.478
1977	24.85957
1978	7.71903
1979	20.61244
1980	36.15544
1981	32.72551
1982	11.61337
1983	-9.20796
1984	-10.70054
1985	-6.5713
1986	-9.08329
1987	-6.27082
1988	-3.87905
1989	-4.3317
1990	8.96157
1991	1.9175
1992	3.12158
1993	0.89866
1994	7.93059
1995	9.63396
1996	13.39183
1997	13.12914
1998	3.17637
1999	11.4869
2000	18.64409
2001	15.70682
2002	17.3048
2003	21.87714
2004	26.88783
2005	32.14741
2006	29.71921
2007	25.01156
2008	28.12037
2009	9.3189
2010	16.58975
2011	26.55496
2012	25.02988
2013	21.12687
2014	13.11011
2015	-5.43265
2016	0.42638
2017	5.40187