| Year | Value | | 2024 | 2.076553879542 | | 2023 | 1.4950681651509 | | 2022 | 5.1798084796706 | | 2021 | 1.181917753398 | | 2020 | 1.7774078380617 | | 2019 | 3.3192537270383 | | 2018 | 0.14797084987711 | | 2017 | 0.5681121170848 | | 2016 | 2.7384120873875 | | 2015 | 0.847389733972 | | 2014 | 1.3418649434016 | | 2013 | 2.7060324287218 | | 2012 | 3.7312095075689 | | 2011 | 5.0687139477799 | | 2010 | 3.9500787592388 | | 2009 | 1.6754958728596 | | 2008 | 11.958620689655 | | 2007 | 4.965976545533 | | 2006 | 3.4834069967787 | | 2005 | 3.104966401483 | | 2004 | 3.1222620469935 | | 2003 | 1.9819673462754 | | 2002 | 0.63761955366632 | | 2001 | 1.7466522498543 | | 1987 | 4.0891164464121 | | 1986 | 18.147633450986 | | 1985 | 2.1289029884807 | | 1984 | 1.8847150257843 | | 1983 | 0.90184289635687 | | 1982 | -2.4107142857234 | | 1981 | 5.7173678537412 | | 1980 | 12.058023572186 |
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