| Year | Value | | 2021 | 5.4899019621174 | | 2020 | -3.72803098534 | | 2019 | 2.2341978350787 | | 2018 | 2.8654596899007 | | 2017 | 2.8858442217955 | | 2016 | 1.0267262583085 | | 2015 | 3.0820265109525 | | 2014 | 3.2577116319462 | | 2013 | 1.5102961439243 | | 2012 | 3.6552219302236 | | 2011 | 2.2440325235758 | | 2010 | 4.4091899040685 | | 2009 | -1.4880969880992 | | 2008 | -2.3705167751447 | | 2007 | 0.52443824149282 | | 2006 | 3.8412677865844 | | 2005 | 2.830254081116 | | 2004 | 3.9749374284775 | | 2003 | 2.0131914921448 | | 2002 | 1.582355732672 | | 2001 | 1.4915318079722 | | 2000 | 4.0324166846206 | | 1999 | 4.2933318164907 | | 1998 | 5.6338688981548 | | 1997 | 5.3342181240524 | | 1996 | 4.1309953298278 | | 1995 | 3.4015813091082 | | 1994 | 4.4573965276246 | | 1993 | 2.2944582931262 | | 1992 | 3.1844172775252 | | 1991 | 0.16422733914514 | | 1990 | 1.150700617558 | | 1989 | 2.3302882974336 | | 1988 | 5.6935479956428 | | 1987 | 3.7451572078249 | | 1986 | 3.388318135581 | | 1985 | 4.216797385109 | | 1984 | 7.8896997874759 | | 1983 | 3.2153820795462 | | 1982 | 0.83698389278581 | | 1981 | 4.1971659246012 | | 1980 | -1.9389206350993 | | 1979 | 0.50203876720761 | | 1978 | 4.9380526435352 | | 1977 | 3.8680777375569 | | 1976 | 5.0751764554846 | | 1975 | 0.11791853536576 | | 1974 | -3.7462859407129 | | 1973 | 5.6045520373187 | | 1972 | 5.5187691853966 | | 1971 | 2.8331654079653 |
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