| Year | Value | | 2023 | 0.28834375291205 | | 2022 | 0.039507866238038 | | 2021 | 0.44119773581631 | | 2020 | 0.68436532538841 | | 2019 | 0.84664672641402 | | 2018 | 0.86631691637084 | | 2017 | 0.98126180450475 | | 2016 | 1.1178572101391 | | 2015 | 1.1912098580702 | | 2014 | 1.2482089973559 | | 2013 | 1.2934470270059 | | 2012 | 1.3287638273375 | | 2011 | 1.3030008548765 | | 2010 | 1.1897877078601 | | 2009 | 2.0761482638464 | | 2008 | 2.0998540325925 | | 2007 | 1.1338554661564 | | 2006 | 1.0985865744181 | | 2005 | 1.0222655923983 | | 2004 | 0.87542728048245 | | 2003 | 0.75765095561691 | | 2002 | 0.74617358271698 | | 2001 | 0.77476593938661 | | 2000 | 0.82151996367421 | | 1999 | 0.87759869985684 | | 1998 | 0.94913814664706 | | 1997 | 0.96467377370423 | | 1996 | 1.0117999166089 | | 1995 | 1.1556661398889 | | 1994 | 1.3484750116345 | | 1993 | 1.5158068925165 | | 1992 | 1.5116285201095 | | 1991 | 1.3304456794304 | | 1990 | 1.3844135015068 | | 1989 | 1.4511522413851 | | 1988 | 1.4332427045018 | | 1987 | 1.5397152259102 | | 1986 | 1.4903050658332 | | 1985 | 1.5455814543386 | | 1984 | 1.6588176323974 | | 1983 | 1.5955274553014 | | 1982 | 1.5822387426651 | | 1981 | 1.5662752500675 | | 1980 | 1.4585192902341 | | 1979 | 1.5796202263132 | | 1978 | 1.6874762361529 | | 1977 | 1.6325107455244 | | 1976 | 1.6033403479609 | | 1975 | 1.683080370471 | | 1974 | 1.8074085083145 |
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