| Year | Value | | 2021 | 2.4165376812613 | | 2020 | -11.429247442324 | | 2019 | 1.5870009924246 | | 2018 | 1.2135495120252 | | 2017 | 2.4822049533553 | | 2016 | 1.3618278055511 | | 2015 | 4.7492122815809 | | 2014 | 4.5645187399516 | | 2013 | 0.9490458203439 | | 2012 | 2.1448139878584 | | 2011 | 2.8909489134086 | | 2010 | 4.7756155355435 | | 2009 | -6.3027271088702 | | 2008 | -1.1771113847606 | | 2007 | 1.9592963343186 | | 2006 | 6.7674696174434 | | 2005 | 0.72177093324434 | | 2004 | 3.0573765904864 | | 2003 | -2.3029247264119 | | 2002 | 0.10903860442153 | | 2001 | 1.2738321351828 | | 2000 | 4.6276593299101 | | 1999 | 5.7098871303219 | | 1998 | 4.7466050691056 | | 1997 | 10.933014870334 | | 1996 | 6.0766227736234 | | 1995 | -11.33736270327 | | 1994 | 7.7136295614572 | | 1993 | -1.0213822642764 | | 1992 | 4.6770372985287 | | 1991 | 8.1035085436742 | | 1990 | 7.3599125284965 | | 1989 | 6.297905290613 | | 1988 | -2.3155863932214 | | 1987 | 4.4666612559988 | | 1986 | -10.992327848155 | | 1985 | 5.2103421151664 | | 1984 | 2.9911622896396 | | 1983 | -12.424764502053 | | 1982 | -6.8007293143569 | | 1981 | 10.359121067788 | | 1980 | 14.48408517029 | | 1979 | 7.4863367112554 | | 1978 | 7.726176573278 | | 1977 | 0.2638446628562 | | 1976 | 3.6501936077584 |
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