| Year | Value | | 2022 | 8.8110920927959 | | 2021 | 8.2430034798181 | | 2020 | 3.7810317991552 | | 2019 | 1.8106037704296 | | 2018 | 3.5644342601351 | | 2017 | 3.2795569467855 | | 2016 | 1.6141660724522 | | 2015 | 0.83674634672456 | | 2014 | 2.9986422612522 | | 2013 | 4.830950967408 | | 2012 | 3.6944970788478 | | 2011 | 5.7967680920653 | | 2010 | 6.3299322014615 | | 2009 | 1.4421513183435 | | 2008 | 10.644621095371 | | 2007 | 6.1435665524805 | | 2006 | 7.5728052385307 | | 2005 | 4.1902026047206 | | 2004 | 51.460859833807 | | 2003 | 27.44971273944 | | 2002 | 5.2233676975945 | | 2001 | 8.8830684881296 | | 2000 | 7.7241356618162 | | 1999 | 6.4705418684693 | | 1998 | 4.8316655859189 | | 1997 | 8.2965675479205 | | 1996 | 5.3992938503892 | | 1995 | 12.535959455896 | | 1994 | 8.2607679857583 | | 1993 | 5.2503388069097 | | 1992 | 4.2590263889339 | | 1991 | 47.079157410536 | | 1990 | 50.462479237852 | | 1989 | 40.6579161175 | | 1988 | 43.863832351505 | | 1987 | 13.550723782782 | | 1986 | 7.6389726657993 | | 1985 | 45.336175553218 | | 1984 | 20.151678105354 | | 1983 | 5.6286232944899 | | 1982 | 7.6462430660615 | | 1981 | 7.5146389069616 | | 1980 | 16.75313568971 | | 1979 | 9.1738051335145 | | 1978 | 3.4778503421218 | | 1977 | 12.853527505429 | | 1976 | 7.7655502392568 | | 1975 | 14.501725743762 | | 1974 | 13.140767371485 | | 1973 | 15.079534916914 | | 1972 | 8.6407315560757 | | 1971 | 3.5800288967813 | | 1970 | 3.8166666664171 | | 1969 | 0.95662806617913 | | 1968 | 0.035976399338231 | | 1967 | 1.2383449887199 | | 1966 | 0.26292725679454 | | 1965 | -1.8916595013061 | | 1964 | 2.1071115013355 | | 1963 | 8.5795996187662 | | 1962 | 9.1571279917707 | | 1961 | -3.9000000009999 | | 1960 | -3.5621917997606 |
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