| Year | Value | | 2023 | 0.89560315551153 | | 2022 | 0.49263501943339 | | 2021 | -1.8759949251038 | | 2020 | -1.7297991991787 | | 2019 | -2.1830559509892 | | 2018 | -1.8845293478673 | | 2017 | 0.90900535013828 | | 2016 | 0.59858980697911 | | 2015 | 0.68582104585837 | | 2014 | -1.0663006531284 | | 2013 | -1.0800356153793 | | 2012 | 0.89533039781617 | | 2011 | 0.29667091312014 | | 2010 | 0.89820138231327 | | 2009 | 1.6491939646865 | | 2008 | 1.8572692661716 | | 2007 | 2.038582251709 | | 2006 | 2.1616868942647 | | 2005 | 2.2828244943995 | | 2004 | 2.3768642848267 | | 2003 | 2.4379466724469 | | 2002 | 2.5120335629778 | | 2001 | 2.590274325927 | | 2000 | 1.7408332787686 | | 1999 | 0.010309101227323 | | 1998 | 0.67464854096707 | | 1997 | 0.36793554948007 | | 1996 | 0.095170123766629 | | 1995 | 0.18702717344934 | | 1994 | 0.4537166430487 | | 1993 | 0.72750054912309 | | 1992 | 1.0351306704224 | | 1991 | 2.1420723012369 | | 1990 | 6.7046967987947 | | 1989 | 11.047225857301 | | 1988 | 12.171291976001 | | 1987 | 13.420983962375 | | 1986 | 14.873594840908 | | 1985 | 16.68631903226 | | 1984 | 19.052110895103 | | 1983 | 20.473238598693 | | 1982 | 11.762953621775 | | 1981 | 2.376374611717 | | 1980 | 2.6584833811061 | | 1979 | 2.8804992396949 | | 1978 | 3.1200763903961 | | 1977 | 3.3509943684775 | | 1976 | 3.5422829842485 | | 1975 | 3.1903797190424 | | 1974 | 2.6563447908721 |
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