| Year | Value | | 2022 | 6.3781469513337 | | 2021 | 2.4107031217436 | | 2020 | -1.755808335176 | | 2019 | 0.53908755919176 | | 2018 | 1.935618931506 | | 2017 | 0.10426207895844 | | 2016 | -3.0782176567693 | | 2015 | 0.983600952697 | | 2014 | 3.5169555136923 | | 2013 | 1.4685651103543 | | 2012 | 4.1776358710252 | | 2011 | 2.7694079414409 | | 2010 | 3.2503440918013 | | 2009 | 0.15693608716869 | | 2008 | 5.5495476938393 | | 2007 | 2.8231037373694 | | 2006 | 2.3956208252917 | | 2005 | 3.8982737075948 | | 2004 | 1.4603681442523 | | 2003 | 1.0342537242623 | | 2002 | 0.25553662691646 | | 2001 | 5.3072208102855 | | 2000 | 3.7107860871361 | | 1999 | 3.5037978410894 | | 1998 | 3.2019434167909 | | 1997 | 0.0055202870547238 | | 1996 | 0.92484260961597 | | 1995 | 5.6296592151238 | | 1994 | 2.8159166515397 | | 1993 | 0.8481815962896 | | 1992 | 5.1388977994483 | | 1991 | 6.1495505311905 | | 1990 | 4.2675566285597 | | 1989 | 4.3726376639733 | | 1988 | 0.82947242564638 | | 1987 | 7.0217530390278 | | 1986 | 2.1902582543313 | | 1985 | 1.4231989823873 | | 1984 | 1.2054841036559 | | 1983 | 1.473058534623 | | 1982 | 4.6140674987309 | | 1981 | 15.124844377035 | | 1980 | 19.477729113291 | | 1979 | 9.3900427128736 | | 1978 | 10.877518292099 | | 1977 | 8.8657319002619 | | 1976 | 9.6691198466874 | | 1975 | 17.742787699652 | | 1974 | 34.220604226879 | | 1973 | 13.440600697174 | | 1972 | 7.8805762890535 | | 1971 | 8.3913452492058 | | 1970 | 13.398762534818 | | 1969 | 2.2543814996892 | | 1968 | 3.9694541053439 | | 1967 | 3.2071790871853 | | 1966 | 2.4790083965773 |
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