| Year | Value | | 2022 | 7.1986161560979 | | 2021 | 3.4669258531315 | | 2020 | 0.37159021232436 | | 2019 | 0.075324135002551 | | 2018 | 1.0903300058187 | | 2017 | 1.0123540331561 | | 2016 | 0.60404908699689 | | 2015 | 0.73138448738859 | | 2014 | 1.1413446753829 | | 2013 | 0.75766918452231 | | 2012 | 1.7297348158144 | | 2011 | 5.1289237668162 | | 2010 | 1.1793357687364 | | 2009 | 1.055950297312 | | 2008 | 6.7079229351594 | | 2007 | 4.5780857237715 | | 2006 | 4.0371235942961 | | 2005 | 4.6909487090377 | | 2004 | 4.4519439239505 | | 2003 | 2.1203909173333 | | 2002 | 1.8655250361008 | | 2001 | 3.7508205747202 | | 2000 | 2.2712875682872 | | 1999 | 0.51482713019299 | | 1998 | 2.5470597755415 | | 1997 | 4.490136278552 | | 1996 | 9.7889204017997 | | 1995 | 10.029656450102 | | 1994 | 10.585806652645 | | 1993 | 18.506688330271 | | 1992 | 11.214481380199 | | 1991 | 14.402674880627 | | 1990 | 23.999165113086 | | 1989 | 17.634079938535 | | 1988 | 19.761161785886 | | 1987 | 24.864500337312 | | 1986 | 31.935016147276 | | 1985 | 22.328375055442 | | 1984 | 11.507169505731 | | 1983 | 13.314317730352 | | 1982 | 11.728886865468 | | 1981 | 14.797151629973 | | 1980 | 17.366968256403 | | 1979 | 14.056024736106 | | 1978 | 13.275123292138 | | 1977 | 11.820277539149 | | 1976 | 7.0346896319883 | | 1975 | 19.088499654386 | | 1974 | 16.899036842235 | | 1973 | 6.3919742031183 | | 1972 | 1.5352153667887 | | 1971 | 0.44580866769247 | | 1970 | 2.8178539220851 | | 1969 | 0.19499025003815 | | 1968 | 2.537680713488 | | 1967 | 1.4669163547238 | | 1966 | -1.1873554359338 | | 1965 | 0.45697467291712 | | 1964 | 1.7575662040575 | | 1963 | 1.5690041625892 | | 1962 | 0.096153846394794 | | 1961 | -2.6824703680742 | | 1960 | 0.03897419900307 |
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