| Year | Value | | 2018 | 0.835634262572 | | 2017 | 3.1210281564356 | | 2016 | 1.8263286711339 | | 2015 | 2.943578129089 | | 2014 | 4.1955383032117 | | 2013 | 1.6574732897697 | | 2012 | 0.24432082187818 | | 2011 | 0.93127250686504 | | 2010 | 4.295928573419 | | 2009 | -3.5272540539319 | | 2008 | -2.4452174360628 | | 2007 | 1.8829067249798 | | 2006 | 0.26987630365622 | | 2005 | 3.0557360851531 | | 2004 | 2.5140976675922 | | 2003 | 3.55338060694 | | 2002 | 2.8916059306293 | | 2001 | 2.8639523173168 | | 2000 | 4.037184288463 | | 1999 | 1.813370206162 | | 1998 | 6.4525503373844 | | 1997 | 7.1076345602252 | | 1996 | 2.7772106038726 | | 1995 | 2.5096883269789 | | 1994 | 5.8903867479114 | | 1993 | 3.733587109588 | | 1992 | 2.7283710383029 | | 1991 | 0.031249481100247 | | 1990 | 0.80946670859578 | | 1989 | 2.1184819503927 | | 1988 | 5.691128260415 | | 1987 | 4.3603684578022 | | 1986 | 5.8332876156639 | | 1985 | 2.9471341960799 | | 1984 | 1.9447629459175 | | 1983 | 4.0407329902567 | | 1982 | 2.035868130678 | | 1981 | -1.1332614835509 | | 1980 | -1.3366079727963 | | 1979 | 1.0815193436318 | | 1978 | 4.9843451585425 | | 1977 | 0.61439783775398 | | 1976 | 1.2341840747868 | | 1975 | 0.9442371678214 | | 1974 | -6.1794725139338 | | 1973 | 3.8592720769582 | | 1972 | 3.6204456054903 | | 1971 | 1.5954825497374 |
|