| Year | Value | | 2021 | 4.7837501803438 | | 2020 | -4.9321328028859 | | 2019 | 1.5479239994915 | | 2018 | 1.9546083606208 | | 2017 | 2.6054220959961 | | 2016 | 1.6488228680626 | | 2015 | 3.0476606378531 | | 2014 | 2.4933124854121 | | 2013 | 1.3316724025392 | | 2012 | 1.7140059687792 | | 2011 | 1.3911494491148 | | 2010 | 3.9199028225603 | | 2009 | -2.7016818573141 | | 2008 | -2.188031982208 | | 2007 | 1.5233608663295 | | 2006 | 3.06094400187 | | 2005 | 2.324556269822 | | 2004 | 3.3423296830824 | | 2003 | 1.8319679455703 | | 2002 | 1.3453305668847 | | 2001 | 1.6523303740322 | | 2000 | 3.4641350608493 | | 1999 | 3.159694817273 | | 1998 | 3.5623262438579 | | 1997 | 3.7732943752688 | | 1996 | 3.1439438498529 | | 1995 | 3.1881079731213 | | 1994 | 3.7409780623145 | | 1993 | 0.84166926682225 | | 1992 | 2.0614041451014 | | 1991 | 1.3043379549247 | | 1990 | 2.5138837289297 | | 1989 | 3.0726748408222 | | 1988 | 5.5157673575013 | | 1987 | 3.6876955721405 | | 1986 | 4.4345107814121 | | 1985 | 3.8575833966274 | | 1984 | 5.2250305215628 | | 1983 | 2.8100231662363 | | 1982 | 1.2670115952424 | | 1981 | 1.7546606815572 | | 1980 | 0.95664115251434 | | 1979 | 1.4637074212604 | | 1978 | 4.6940128358397 | | 1977 | 3.3689765929096 | | 1976 | 4.7502597855523 | | 1975 | 0.37608970838983 | | 1974 | -2.4961467081259 | | 1973 | 5.6326740155607 | | 1972 | 5.4583479780615 | | 1971 | 3.1901487291869 |
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