| Year | Value | | 2024 | 7.3226516518129 | | 2023 | 0.048970850901449 | | 2022 | 5.907018249571 | | 2021 | -10.927442433559 | | 2020 | 5.7257154484169 | | 2019 | 2.2196221002893 | | 2018 | 1.3621056096195 | | 2017 | 2.7359029332087 | | 2016 | 5.4997297695871 | | 2015 | 8.5817330617329 | | 2014 | 11.581714781494 | | 2013 | 10.67212639764 | | 2012 | 5.8380001021633 | | 2011 | 0.48920489482529 | | 2010 | 0.49160987923791 | | 2009 | 12.002169054288 | | 2008 | 16.607236183952 | | 2007 | 21.700342942038 | | 2006 | 16.433256793856 | | 2005 | 6.5169357689098 | | 2004 | 3.7751170235384 | | 2003 | 4.5996567071259 | | 2002 | 4.7924052193601 | | 2001 | 4.9803399965803 | | 2000 | 5.1684319967899 | | 1999 | 5.3590237539435 | | 1998 | 5.3131748716712 | | 1997 | 3.9802608125232 | | 1996 | 2.8168986677208 | | 1995 | 2.9329848722687 | | 1994 | 3.0315206362832 | | 1993 | 3.1207665229048 | | 1992 | 3.2028351218447 | | 1991 | 3.2801914714773 | | 1990 | 3.3564360218821 | | 1989 | 3.4372670840348 | | 1988 | 3.5286468987019 | | 1987 | 3.7424164163186 | | 1986 | 4.4055325366713 | | 1985 | 5.061754194027 | | 1984 | 5.3641396347815 | | 1983 | 5.6692335978317 | | 1982 | 5.9459909087978 | | 1981 | 6.197260354764 | | 1980 | 6.4532480604385 | | 1979 | 6.7409095202251 | | 1978 | 7.0777755502111 | | 1977 | 7.4783242479631 | | 1976 | 7.9442160308585 | | 1975 | 8.4948022793186 |
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