| Year | Value | | 2022 | 6.8851282334429 | | 2021 | 4.2610512742281 | | 2020 | 3.2144406219734 | | 2019 | 3.6999839800861 | | 2018 | 3.7518618670451 | | 2017 | 4.4245365518254 | | 2016 | 4.4484419994283 | | 2015 | 2.3887203283955 | | 2014 | 3.4183616966296 | | 2013 | 4.3433713127952 | | 2012 | 3.7818075467969 | | 2011 | 6.2141239306709 | | 2010 | 3.8595090983317 | | 2009 | 1.8591025473302 | | 2008 | 11.355761126315 | | 2007 | 6.8216175359032 | | 2006 | 6.5608528279538 | | 2005 | 9.1086498571922 | | 2004 | 7.5786224730973 | | 2003 | 5.6034767543447 | | 2002 | 8.1326305428105 | | 2001 | 7.2858736661013 | | 2000 | 5.9775773473714 | | 1999 | 5.2136105860112 | | 1998 | 6.6134607051806 | | 1997 | 9.2329029488494 | | 1996 | 11.056916532199 | | 1995 | 8.4114131227057 | | 1994 | 10.855321149439 | | 1993 | 11.819690174626 | | 1992 | 10.045917998409 | | 1991 | 33.166421916753 | | 1990 | 41.221867138097 | | 1989 | 11.387132199796 | | 1988 | 10.832703768991 | | 1987 | 12.323213275505 | | 1986 | 36.931121296502 | | 1985 | 18.686791297124 | | 1984 | 3.4067501183779 | | 1983 | 4.5386781513326 | | 1982 | 0.30738556143707 | | 1981 | 11.43306795035 | | 1980 | 10.823843233541 | | 1979 | 11.343385881161 | | 1978 | 8.2879762495771 | | 1977 | 12.3245796861 | | 1976 | 10.72499999925 | | 1975 | 13.159244379858 | | 1974 | 16.494896689013 | | 1973 | 13.796033994502 | | 1972 | 0.52970325232307 | | 1971 | 0.45359188076381 | | 1970 | 2.3443393488142 | | 1969 | 2.0972806447157 | | 1968 | 1.9263285023009 | | 1967 | 0.48543689344875 | | 1966 | 0.68426197446523 | | 1965 | 0.80000000000354 | | 1964 | 0.19356399703655 | | 1963 | 0.15145089937591 | | 1962 | 2.052550232097 | | 1961 | 0.55333538272651 | | 1960 | -1.19069315346 |
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