| Year | Value | | 2022 | 1.0721673814229 | | 2021 | 1.1651358486026 | | 2020 | 1.1600576973973 | | 2019 | 1.1324421619568 | | 2018 | 1.221445659216 | | 2017 | 1.3104826630319 | | 2016 | 1.3340851574389 | | 2015 | 1.3497900203624 | | 2014 | 1.3977751944463 | | 2013 | 1.4304997159645 | | 2012 | 1.4492841933337 | | 2011 | 1.4538734073168 | | 2010 | 1.4572298835144 | | 2009 | 1.5078919487324 | | 2008 | 1.6566390573139 | | 2007 | 1.7432556185774 | | 2006 | 1.7302696916773 | | 2005 | 1.7531759490284 | | 2004 | 1.7723319460687 | | 2003 | 1.7825762292865 | | 2002 | 1.7959298791696 | | 2001 | 1.7938143339827 | | 2000 | 1.830648178896 | | 1999 | 1.951251573448 | | 1998 | 2.0563612755248 | | 1997 | 2.2018666803053 | | 1996 | 2.3807325984787 | | 1995 | 2.627508394049 | | 1994 | 3.7629422779542 | | 1993 | 5.2646279586557 | | 1992 | 4.836681183643 | | 1991 | 3.8370225801223 | | 1990 | 3.8888910533693 | | 1989 | 3.5768104956227 | | 1988 | 3.6221401701927 | | 1987 | 4.0202603714537 | | 1986 | 3.794021317354 | | 1985 | 3.3385758634098 | | 1984 | 3.5954143571751 | | 1983 | 3.8853885072104 | | 1982 | 3.9318625721521 | | 1981 | 2.6349900187822 | | 1980 | 2.4024304354626 | | 1979 | 1.5086441541694 | | 1978 | -1.3165998477281 | | 1977 | -4.3242843772044 | | 1976 | -6.4586858181263 | | 1975 | -2.7196385198493 | | 1974 | 0.88695959743953 | | 1973 | 1.2640335472123 | | 1972 | 1.0394063900827 | | 1971 | 0.18203865436027 | | 1970 | 0.43048316386518 | | 1969 | 1.9134680496329 | | 1968 | 1.951808530376 | | 1967 | 1.9994104512672 | | 1966 | 2.0610744528449 | | 1965 | 2.1272425273827 | | 1964 | 2.1275922831048 | | 1963 | 2.1333966538658 | | 1962 | 2.1688528706123 | | 1961 | 2.19488337445 |
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