| Year | Value | | 2022 | 18.800878666495 | | 2021 | 8.4045384507634 | | 2020 | 7.3211064341552 | | 2019 | 0.68677217079736 | | 2018 | -2.8146980766847 | | 2017 | 16.052535303039 | | 2016 | 5.5576896140097 | | 2015 | 5.5446889125978 | | 2014 | 4.4053523418529 | | 2013 | 7.9379580749242 | | 2012 | 18.161045306545 | | 2011 | 9.5921660597967 | | 2010 | 6.4932659147399 | | 2009 | 10.555435529953 | | 2008 | 24.406951035391 | | 2007 | 8.4120628577254 | | 2006 | 2.7454200021424 | | 2005 | 13.252069918822 | | 2004 | 8.1764293748205 | | 2003 | 10.647464565831 | | 2002 | -1.3656800532806 | | 2001 | 9.2961877134189 | | 2000 | 24.432024210215 | | 1999 | 3.3854242734046 | | 1998 | 12.500410765338 | | 1997 | 31.111589831969 | | 1996 | 26.436781609195 | | 1995 | 19.263253638254 | | 1994 | 14.852814983397 | | 1993 | 9.6793465806793 | | 1992 | 1.8233333333331 | | 1991 | 8.9969387349433 | | 1990 | 7.0021695665112 | | 1989 | 11.661599847996 | | 1988 | 4.4867976970418 | | 1987 | 7.1132376395534 | | 1986 | 1.6756756756755 | | 1985 | 3.8042868364943 | | 1984 | 14.316869788326 | | 1983 | 8.1512313562263 | | 1982 | 5.8680963572266 | | 1981 | 12.167394348794 | | 1980 | 2.4985195003017 | | 1979 | 36.540756998092 | | 1978 | 23.89562064693 | | 1977 | 6.8345140413649 | | 1976 | 6.8565515736454 | | 1975 | 15.709874598823 | | 1974 | 15.722307299094 | | 1973 | 6.0064935067531 | | 1972 | 3.8285576691733 | | 1971 | 3.8509627404445 | | 1970 | 0.19965061143023 | | 1969 | 4.0238836973312 | | 1968 | 6.0572687222252 | | 1967 | -1.0893246187425 | | 1966 | 4.4368600676909 |
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