| Year | Value | | 2022 | 1.4663337564366 | | 2021 | 1.5606112441555 | | 2020 | 1.8245782648611 | | 2019 | 1.8404977696963 | | 2018 | 1.9993940110556 | | 2017 | 2.2707824955263 | | 2016 | 1.9639130924056 | | 2015 | 1.8657579632644 | | 2014 | 1.9537973727918 | | 2013 | 2.0265093472265 | | 2012 | 2.1482282400354 | | 2011 | 2.2555537754993 | | 2010 | 3.1625198679545 | | 2009 | 2.722681670282 | | 2008 | 1.547920805645 | | 2007 | 2.3681545861109 | | 2006 | 2.0742249906691 | | 2005 | 2.0492596155836 | | 2004 | 2.1316629381283 | | 2003 | 2.3690009191646 | | 2002 | 2.5163929527429 | | 2001 | 2.7441780229937 | | 2000 | 3.2849261283703 | | 1999 | 3.5624511916697 | | 1998 | 2.8519284665319 | | 1997 | 2.7121773472999 | | 1996 | 2.8246736630959 | | 1995 | 3.2418893764196 | | 1994 | 2.7411224099601 | | 1993 | 2.4754726625897 | | 1992 | 2.7064535247623 | | 1991 | 2.8888469554113 | | 1990 | 3.550475988308 | | 1989 | 4.3077146593055 | | 1988 | 3.3697552447552 | | 1987 | 4.1813130740447 | | 1986 | 4.8399873257288 | | 1985 | 4.3140990745781 | | 1984 | 3.9791437980241 | | 1983 | 4.0130568356375 | | 1982 | 4.3577366586216 | | 1981 | 3.3115103532278 | | 1980 | 3.1585365853658 | | 1979 | 1.8512075317233 | | 1978 | 1.5056082830026 | | 1977 | 1.4381320642475 | | 1976 | 1.5517912772586 |
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