Year	Percent
1981	-47.16286
1982	-38.19881
1983	-35.8136
1984	-35.89202
1985	-41.47684
1986	-51.2149
1987	-41.45896
1988	-37.57352
1989	-31.3906
1990	-22.07249
1991	-28.46687
1992	-7.42966
1993	-11.07768
1994	-9.89591
1995	-1.02091
1996	-6.92542
1997	5.34124
1998	-11.66418
1999	-11.92446
2000	-13.89311
2001	-15.18164
2002	-17.06402
2003	-15.59529
2004	-9.75377
2005	-4.84269
2006	5.95655
2007	1.34847
2008	-13.16394
2009	-7.25776
2010	-9.99207
2011	-21.89212
2012	-22.44426
2013	-22.53151
2014	-4.82431
2015	1.00418
2016	4.79191
2017	2.35316