Year	Percent
1967	4.24178
1968	2.73481
1969	4.10566
1970	5.22593
1971	6.92244
1972	-4.90581
1973	26.44854
1974	31.08616
1975	20.7427
1976	11.13113
1977	12.4865
1978	26.5751
1979	15.73694
1980	18.28801
1981	8.32434
1982	8.31479
1983	16.9606
1984	35.9192
1985	28.52885
1986	26.86112
1987	10.82259
1988	12.05558
1989	12.36922
1990	25.11711
1991	43.84229
1992	60.03573
1993	52.8064
1994	31.10725
1995	25.18685
1996	18.87211
1997	9.6087
1998	10.57507
1999	6.91606
2000	10.58708
2001	7.80737
2002	9.08385
2003	11.62406
2004	12.8586
2005	11.46874
2006	8.84819
2007	11.32081
2008	13.54681
2009	11.64617
2010	9.81148
2011	5.76779
2012	6.57072
2013	8.39805
2014	7.01231
2015	6.61612
2016	4.59539
2017	6.95456