| Year | Value | | 2022 | 33.88987971009 | | 2021 | 26.839522155772 | | 2020 | 20.356346855906 | | 2019 | 15.809632171934 | | 2018 | 13.833035658666 | | 2017 | 10.687115028424 | | 2016 | 6.6281333723092 | | 2015 | 9.5688995596862 | | 2014 | 6.8900195159719 | | 2013 | 7.4640219294452 | | 2012 | 23.600417677317 | | 2011 | 33.249959882334 | | 2010 | 8.1492640296508 | | 2009 | 8.4836440453028 | | 2008 | 44.356685876695 | | 2007 | 17.24040083409 | | 2006 | 12.299476311483 | | 2005 | 9.9699712351289 | | 2004 | 3.3273704789485 | | 2003 | 13.674045202827 | | 2002 | 0.6750891021708 | | 2001 | -8.2378445339114 | | 2000 | 0.66245810926648 | | 1999 | 7.9414486413732 | | 1998 | 0.89480169396411 | | 1997 | 2.3952095808383 | | 1996 | -8.4842486894883 | | 1995 | 10.022173355324 | | 1994 | 7.5938760018534 | | 1993 | 3.5430659616603 | | 1992 | 10.527444011959 | | 1991 | 35.722598229872 | | 1990 | 5.1524812417477 | | 1989 | 7.8173011822305 | | 1988 | 7.0807153214109 | | 1987 | -2.4286724828337 | | 1986 | -9.8087650705066 | | 1985 | 19.064685144441 | | 1984 | 8.4172737831205 | | 1983 | 0.67537806485472 | | 1982 | 5.8900610772396 | | 1981 | 6.1359671868043 | | 1980 | 4.4825378060044 | | 1979 | 16.032235939652 | | 1978 | 14.308114464915 | | 1977 | 16.65713959085 | | 1976 | 28.537839823785 | | 1975 | 6.550104383942 | | 1974 | 8.5921559739109 | | 1973 | 8.9135802469581 | | 1972 | -6.0815119717913 | | 1971 | 0.53622428169519 | | 1970 | 10.121951219564 | | 1969 | 1.4256884314863 | | 1968 | 0.182612665559 | | 1967 | 0.80867850105468 | | 1966 | -1.3618677046691 |
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