| Year | Value | | 2022 | 2.4740737192537 | | 2021 | 3.0632898894155 | | 2020 | 3.4454582595669 | | 2019 | -2.0933333333333 | | 2018 | 2.4581415800753 | | 2017 | 0.83819457967502 | | 2016 | 2.0688403605347 | | 2015 | 1.2060732215011 | | 2014 | 2.2362903153698 | | 2013 | 3.5325247069492 | | 2012 | 2.8662688748991 | | 2011 | 5.8262160883886 | | 2010 | 5.3394168063745 | | 2009 | 5.0572231469363 | | 2008 | 9.8702479127599 | | 2007 | 4.1678233011998 | | 2006 | 2.2090240787118 | | 2005 | 0.47923039782608 | | 2004 | 0.51550676699808 | | 2003 | 0.61219439512521 | | 2002 | 0.24718651429923 | | 2001 | -1.1209447745718 | | 2000 | -1.1249947785477 | | 1999 | -1.3337635022942 | | 1998 | 0.37126973498381 | | 1997 | 0.05715470377076 | | 1996 | 1.2220698845131 | | 1995 | 4.8684310305603 | | 1994 | 0.56432547853314 | | 1993 | 1.0557953144269 | | 1992 | 0.077006006469078 | | 1991 | 4.8611111111114 | | 1990 | 2.0771513353116 | | 1989 | 1.0326449033974 | | 1988 | 0.90756302521051 | | 1987 | -1.5471167369902 | | 1986 | -3.203331464723 | | 1985 | -3.0587687291366 | | 1984 | -1.559037065342 | | 1983 | 0.19142419601903 | | 1982 | 1.0210396039604 | | 1981 | 2.7989821882949 | | 1980 | 4.1692665536329 | | 1979 | 1.0815669028834 | | 1978 | -1.5836018502208 | | 1977 | 11.399011169953 | | 1976 | 31.558660564113 | | 1975 | 34.576106338148 | | 1974 | 21.437007873664 | | 1973 | 16.513761468195 | | 1972 | 4.3311797078349 | | 1971 | 4.47499999975 | | 1970 | 0.17777777777779 | | 1969 | 3.4958601655933 | | 1968 | 1.5887850467294 | | 1967 | 2.0992366421952 | | 1966 | 1.5503875959305 | | 1965 | 0.38910505934226 | | 1964 | 2.7999999989998 |
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