| Year | Value | | 2024 | 2.8365731724352 | | 2023 | 2.135593849814 | | 2022 | 1.435704370487 | | 2021 | 2.3560977917918 | | 2020 | 3.1536092029197 | | 2019 | 2.9843891362197 | | 2018 | 2.9108095986138 | | 2017 | 2.8083373080547 | | 2016 | 2.5357199183396 | | 2015 | 3.1199592414691 | | 2014 | 3.6325188465201 | | 2013 | 3.418226675846 | | 2012 | 4.0478625631564 | | 2011 | 3.6915030839185 | | 2010 | 2.9346867017347 | | 2009 | 3.6463809081325 | | 2008 | 2.1865461816298 | | 2007 | 1.8925975396006 | | 2006 | 4.0927020165635 | | 2005 | 3.5192169604259 | | 2004 | 3.5758348539816 | | 2003 | 6.1451940018851 | | 2002 | 5.2520295852783 | | 2001 | 0.76200489689889 | | 2000 | 1.2121759760185 | | 1999 | 3.7281160396477 | | 1998 | 3.7646866376293 | | 1997 | 3.8045080344582 | | 1996 | 4.0054046735712 | | 1995 | 4.8936801197316 | | 1994 | 8.38872960213 | | 1993 | 11.807259107171 | | 1992 | 8.156419410481 | | 1991 | 1.5913258836483 | | 1990 | 1.4345882114784 | | 1989 | 2.9987647953118 | | 1988 | 1.1826711465394 | | 1987 | 0.28284965138429 | | 1986 | 0.059334023306695 | | 1985 | 2.0925752394436 | | 1984 | 2.4629117200788 | | 1983 | 0.66999925658612 | | 1982 | -8.2580343853674 | | 1981 | -9.8197707393124 | | 1980 | -3.6258078797891 | | 1979 | 0.32365882256068 | | 1978 | 2.0086978543684 | | 1977 | 2.1280995644747 | | 1976 | 2.213446083287 |
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