| Year | Value | | 2022 | 33.98393194707 | | 2021 | 16.841524019878 | | 2020 | 22.796311364253 | | 2019 | 18.703782567251 | | 2018 | 12.481411117043 | | 2017 | 10.680088724258 | | 2016 | 11.502907394267 | | 2015 | 6.7318406965899 | | 2014 | 3.4381665995861 | | 2013 | 4.7650240477913 | | 2012 | 5.0180415542925 | | 2011 | 6.3327948384904 | | 2010 | 4.8273419007468 | | 2009 | 0.39388604017341 | | 2008 | 15.281774482377 | | 2007 | 6.5572277263806 | | 2006 | 11.34521522443 | | 2005 | 13.973008326384 | | 2004 | 21.031833927722 | | 2003 | 28.699577788737 | | 2002 | 7.032874062246 | | 2001 | 13.31672224251 | | 2000 | 9.3332219756563 | | 1999 | 3.0043942155072 | | 1998 | 5.2690354704217 | | 1997 | 20.559007339583 | | 1996 | 20.583596214511 | | 1995 | 27.60818517276 | | 1994 | 39.331619537275 | | 1993 | 29.705971506517 | | 1992 | 19.358494654122 | | 1991 | 15.419907366949 | | 1990 | 21.276032006783 | | 1989 | 6.9239050371124 | | 1988 | 4.1054680587506 | | 1987 | -11.44946461217 | | 1986 | 3.2799266336662 | | 1985 | 10.648839013893 | | 1984 | 6.4020323910607 | | 1983 | 10.243663352654 | | 1982 | 7.3592422760505 | | 1981 | 10.858333333 | | 1980 | 17.778305245658 | | 1979 | 13.093924299819 | | 1978 | -2.6735949836929 | | 1977 | 6.4919005811334 | | 1976 | 7.0381522782362 | | 1975 | 16.773570324582 | | 1974 | 14.950697343972 | | 1973 | 22.738919478919 | | 1972 | 3.1896939691794 | | 1971 | 9.5795832822563 | | 1970 | 1.3684934073667 | | 1969 | 1.4131812420197 | | 1968 | 1.3162118782736 | | 1967 | -2.9353109810065 | | 1966 | 8.3018358533231 | | 1965 | 2.2639425728972 | | 1964 | 9.1621458712944 | | 1963 | 4.3068217543596 | | 1962 | 0.55490425986951 | | 1961 | 3.7797063834267 | | 1960 | -5.0300415959369 |
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