| Year | Value | | 2021 | 0.8051833911794 | | 2020 | 0.85370787812898 | | 2019 | 0.88792529334164 | | 2018 | 0.95429191789132 | | 2017 | 1.2240337581812 | | 2016 | 1.3376347795002 | | 2015 | 2.2297950532192 | | 2014 | 1.5553957091151 | | 2013 | 1.8468760929651 | | 2012 | 0.98098019012832 | | 2011 | -2.6286563552168 | | 2010 | 2.7923290692913 | | 2009 | 0.39253094807516 | | 2008 | 2.236282715432 | | 2007 | 0.5105149828435 | | 2006 | 2.0805967352947 | | 2005 | 0.46330821445856 | | 2004 | 0.37033493455879 | | 2003 | -1.1315164207039 | | 2002 | 3.0573853261095 | | 2001 | 0.087474517845806 | | 2000 | 0.89265856676617 | | 1999 | 1.9641963670502 | | 1998 | 1.9556861897417 | | 1997 | 1.1734536483024 | | 1996 | 1.4671930264195 | | 1995 | 1.4701720897137 | | 1994 | 2.6657684725925 | | 1993 | 2.0837583394622 | | 1992 | 0.45891781792727 | | 1991 | 1.3319620124615 | | 1990 | 0.49035966552071 | | 1989 | 0.59744090932312 | | 1988 | 0.37303145534342 | | 1987 | 4.2451081751785 | | 1986 | 0.62339769179054 | | 1985 | 0.81101697987733 | | 1984 | 0.59201115160575 | | 1983 | 0.12116694557264 | | 1982 | 0.58856672146448 | | 1981 | 1.2160783348047 | | 1980 | 0.91308883094718 | | 1979 | 0.85873192637959 | | 1978 | 0.58740163733346 | | 1977 | 2.0967323029657 | | 1976 | 2.0235088902115 | | 1975 | 2.311817635199 | | 1974 | 1.8201479591641 | | 1973 | 1.5285319871711 | | 1972 | 2.4097116264516 | | 1971 | 2.0223229494998 | | 1970 | 2.3310638851647 | | 1969 | 2.3788791235406 | | 1968 | 2.4208218643987 | | 1967 | 2.4582923348898 | | 1966 | 2.4928784956222 | | 1965 | 2.5112700815075 | | 1964 | 2.5051037854985 | | 1963 | 2.5422248286535 | | 1962 | 2.6528341285169 | | 1961 | 2.8114253994075 |
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