| Year | Value | | 2022 | 4.5201926639496 | | 2021 | 0.15585572213152 | | 2020 | -2.5952432588738 | | 2019 | 1.7731018246028 | | 2018 | 4.0814763764453 | | 2017 | 3.3475783475784 | | 2016 | 3.8632253822127 | | 2015 | 1.3748854262144 | | 2014 | 0.51930647457919 | | 2013 | 2.91354193604 | | 2012 | 3.4233752340198 | | 2011 | 7.2781178270849 | | 2010 | 3.6890122967077 | | 2009 | 3.1310355901596 | | 2008 | 7.7322785791842 | | 2007 | 4.8037064130699 | | 2006 | 2.4908363878708 | | 2005 | 2.3657645383043 | | 2004 | 2.827485193912 | | 2003 | 4.1727477776304 | | 2002 | 0.76203208556119 | | 2001 | 4.2726702446511 | | 2000 | 1.0921645997739 | | 1999 | 1.9686736600092 | | 1998 | 5.7116816041312 | | 1997 | 3.3681400643794 | | 1996 | 3.050161812298 | | 1995 | 2.1656472144153 | | 1994 | 0.81666666666703 | | 1993 | 5.2065892519577 | | 1992 | 4.8830227156861 | | 1991 | 6.4973455598455 | | 1990 | 8.1913713204097 | | 1989 | 6.1893540338235 | | 1988 | 11.758326878389 | | 1987 | 5.6637747585522 | | 1986 | 1.798842484338 | | 1985 | 4.4209723962191 | | 1984 | 5.2912176107243 | | 1983 | 6.7041839980142 | | 1982 | 7.0315568938948 | | 1981 | 11.180666763762 | | 1980 | 14.492874406452 | | 1979 | 7.8067582495211 | | 1978 | 6.108071005015 | | 1977 | 7.0063044498393 | | 1976 | 11.432436426469 | | 1975 | 13.064880982982 | | 1974 | 14.498469507888 | | 1973 | 11.08531820634 | | 1972 | 21.978504057907 | | 1971 | 9.138193688792 | | 1970 | 4.1241785633357 |
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