| Year | Value | | 2022 | 18.847187784327 | | 2021 | 16.952845722161 | | 2020 | 13.24602342766 | | 2019 | 11.396422337812 | | 2018 | 12.095106517343 | | 2017 | 16.502266213964 | | 2016 | 15.696812638797 | | 2015 | 9.009434980077 | | 2014 | 8.0474108796791 | | 2013 | 8.4955183826568 | | 2012 | 12.224241302058 | | 2011 | 10.826137188002 | | 2010 | 13.740052136369 | | 2009 | 12.537827730469 | | 2008 | 11.581075174825 | | 2007 | 5.3880079685863 | | 2006 | 8.2252215201705 | | 2005 | 17.863493366161 | | 2004 | 14.998033818325 | | 2003 | 14.031783613144 | | 2002 | 12.87657920311 | | 2001 | 18.873646209386 | | 2000 | 6.9332921556516 | | 1999 | 6.6183733947976 | | 1998 | 9.996378123868 | | 1997 | 8.5298742138364 | | 1996 | 29.268292682927 | | 1995 | 72.835502297264 | | 1994 | 57.031708911966 | | 1993 | 57.165252834922 | | 1992 | 44.588842715023 | | 1991 | 13.006973103743 | | 1990 | 7.3644003055769 | | 1989 | 50.466688123592 | | 1988 | 54.511224779767 | | 1987 | 11.290322580645 | | 1986 | 5.717151454363 | | 1985 | 7.4353448275863 | | 1984 | 17.820533286084 | | 1983 | 23.212331551156 | | 1982 | 7.6977472471425 | | 1981 | 20.812822912195 | | 1980 | 9.9722619900143 | | 1979 | 11.709730621212 | | 1978 | 21.709245741666 | | 1977 | 15.087834057269 | | 1976 | 24.3 | | 1975 | 33.964188322178 | | 1974 | 12.674393177433 | | 1973 | 5.4026644539422 | | 1972 | 3.457649752015 | | 1971 | 15.999114848224 | | 1970 | 13.757079924793 | | 1969 | 10.155979202822 | | 1968 | 0.47605905906083 | | 1967 | -3.7263367651421 | | 1966 | 9.6903460837512 | | 1965 | 4.1034587381162 | | 1964 | 0.85679314573755 | | 1963 | -2.6946553523273 | | 1962 | 5.2656323462173 | | 1961 | 6.2791472347751 | | 1960 | 5.4443273618724 |
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