| Year | Value | | 2022 | 2.3965348317847 | | 2021 | 0.61981031566781 | | 2020 | 2.2112076775236 | | 2019 | 3.9313563185072 | | 2018 | 3.4919554030253 | | 2017 | 2.738662855893 | | 2016 | 2.2886154406437 | | 2015 | 2.3863953634581 | | 2014 | 1.9967544083193 | | 2013 | 1.4040502758129 | | 2012 | 0.89920921190226 | | 2011 | 0.42370088519529 | | 2010 | 0.49118281065151 | | 2009 | 0.75390693103197 | | 2008 | 0.65065546056517 | | 2007 | 0.3487550823699 | | 2006 | 0.36433694716294 | | 2005 | 0.63743691820284 | | 2004 | 0.67162845452858 | | 2003 | 0.65773233439155 | | 2002 | 0.74550692112717 | | 2001 | 0.75110649818537 | | 2000 | 0.64526723090085 | | 1999 | 0.5928607739798 | | 1998 | 0.64993627893804 | | 1997 | 0.75679268654029 | | 1996 | 0.65652453359029 | | 1995 | 0.69714300660296 | | 1994 | 0.93526391926236 | | 1993 | 0.99875513202602 | | 1992 | 1.0316402778349 | | 1991 | 2.6950928921179 | | 1990 | 0.97831369927968 | | 1989 | 0.97329458231556 | | 1988 | 0.82103928934608 | | 1987 | 0.68860724821442 | | 1986 | 1.6708981622985 | | 1985 | 1.756748249729 | | 1984 | 0.02087376372126 | | 1983 | 1.4094824928942 | | 1982 | 2.144977411236 | | 1981 | 0.73534023275127 | | 1980 | 1.0486026745129 | | 1979 | 1.013602380839 | | 1978 | 1.0409199036906 | | 1977 | 0.39037559530602 | | 1976 | 0.50885689378148 | | 1975 | 0.73439257976772 | | 1974 | 0.067527758459834 | | 1973 | 0.082692471428403 | | 1972 | 0.082624147474971 | | 1971 | 0.016519368997668 | | 1970 | 0.54370345652293 | | 1969 | -1.1760998027529 | | 1968 | -1.1784784059776 | | 1967 | -1.1647518993493 | | 1966 | -1.1356588932336 | | 1965 | 0.76556892933696 | | 1964 | 0.40385267688212 | | 1963 | 0.41766631990328 | | 1962 | 0.41592912153311 | | 1961 | 0.39889589560516 |
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