| Year | Value | | 2021 | 9.4814426056102 | | 2020 | -5.0994460630125 | | 2019 | 3.6352453518052 | | 2018 | 6.0259752391751 | | 2017 | 7.9755305044236 | | 2016 | 8.6204562411594 | | 2015 | 8.3102259280541 | | 2014 | 6.1704021114647 | | 2013 | 5.8934212937218 | | 2012 | 5.1247354029556 | | 2011 | 4.6485425147817 | | 2010 | 8.2984089069401 | | 2009 | 10.494545228116 | | 2008 | 2.1145919378222 | | 2007 | 7.479784841829 | | 2006 | 7.5509349371829 | | 2005 | 8.2654704389924 | | 2004 | 9.5181209404003 | | 2003 | 8.4711032686067 | | 2002 | 4.373963288269 | | 2001 | 1.5636218853232 | | 2000 | 1.6086270056763 | | 1999 | 2.9872374700536 | | 1998 | 6.4846105532673 | | 1997 | 2.7549623315923 | | 1996 | 10.066982098684 | | 1995 | 4.9958452951397 | | 1994 | 5.2754289893051 | | 1993 | 7.5691200753152 | | 1992 | 4.6001231298168 | | 1991 | 0.043077739816482 | | 1990 | 6.7950206035507 | | 1989 | 5.2324173957334 | | 1988 | 7.5833562381749 | | 1987 | 6.4586339119232 | | 1986 | 4.1191821961585 | | 1985 | 3.6757808616823 | | 1984 | 1.7923677424382 | | 1983 | 10.201371978118 | | 1982 | 1.3140661820993 | | 1981 | 0.63193937346055 | | 1980 | 10.269427829707 | | 1979 | -2.7797493168688 | | 1978 | 7.1265737731074 | | 1977 | 4.8103813701398 | | 1976 | 6.9480583970677 | | 1975 | 5.2617592667827 | | 1974 | -6.4172214497789 | | 1973 | 7.5698890719317 | | 1972 | 0.25683644470799 | | 1971 | 1.4064474757503 |
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