| Year | Value | | 2022 | 7.6507917679853 | | 2021 | 4.1496800336026 | | 2020 | 5.0523665528921 | | 2019 | 5.5686854778493 | | 2018 | 4.0611633875107 | | 2017 | 3.6270961069661 | | 2016 | 8.7903433200463 | | 2015 | 7.868908955909 | | 2014 | 8.3641546965956 | | 2013 | 9.0401631191764 | | 2012 | 9.4598098035713 | | 2011 | 9.2270754612595 | | 2010 | 9.3265041074539 | | 2009 | 11.094823738699 | | 2008 | 9.9078300530648 | | 2007 | 2.2692192443907 | | 2006 | 6.9203358070759 | | 2005 | 6.8363326589288 | | 2004 | 2.8418113124898 | | 2003 | 5.7070093187474 | | 2002 | 3.029399487149 | | 2001 | 2.6883037354563 | | 2000 | 2.4788202070913 | | 1999 | 7.4511126095755 | | 1998 | 11.244467781861 | | 1997 | 4.0099886052318 | | 1996 | 9.2204666237699 | | 1995 | 7.6229695069816 | | 1994 | 8.3492867288339 | | 1993 | 7.5053941908711 | | 1992 | 17.149523624344 | | 1991 | 15.557452927695 | | 1990 | 8.2397003745321 | | 1989 | 8.8468869123255 | | 1988 | 8.9830033820899 | | 1987 | 10.750328044985 | | 1986 | 18.99894955024 | | 1985 | 8.0526412661963 | | 1984 | 2.8457849571627 | | 1983 | 12.377238078271 | | 1982 | 11.698546592414 | | 1981 | 11.144856727844 | | 1980 | 14.684502776377 | | 1979 | 3.5654537852024 | | 1978 | 7.346091250833 | | 1977 | 9.8988528431348 | | 1976 | -3.1132357332719 | | 1975 | 7.5859852135296 | | 1974 | 19.806338028085 | | 1973 | 11.42977252586 | | 1972 | 8.3890238963018 | | 1971 | -1.9995038452083 | | 1970 | 15.237278445036 | | 1969 | 4.0575916228156 | | 1968 | 1.1798699737005 | | 1967 | -2.8083313833469 | | 1966 | 14.388970686866 | | 1965 | 8.4718693284647 |
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