| Year | Value | | 2021 | 2.8383211647962 | | 2020 | 0.075063829215779 | | 2019 | 5.1510823413835 | | 2018 | 1.954881704483 | | 2017 | 5.2541844789075 | | 2016 | 5.0468881261755 | | 2015 | 4.1993005822524 | | 2014 | 3.3891779249254 | | 2013 | 6.4594088437337 | | 2012 | 1.9154558754164 | | 2011 | 4.3273911348425 | | 2010 | 2.6971990043911 | | 2009 | 4.5696934834951 | | 2008 | -4.3345485537395 | | 2007 | 6.1136107120932 | | 2006 | 1.1523041038766 | | 2005 | 1.6341630683296 | | 2004 | 3.2820781566632 | | 2003 | 7.6015340234475 | | 2002 | 4.9712809538511 | | 2001 | 6.4250695859881 | | 2000 | 2.5680476705971 | | 1999 | 2.9779404320111 | | 1998 | 2.671605675874 | | 1997 | 4.1213929504857 | | 1996 | 1.8156459660011 | | 1995 | 4.6873991426617 | | 1994 | 6.8799467329387 | | 1993 | 6.6247936408216 | | 1992 | 1.3966302567348 | | 1991 | -5.6704443660623 | | 1990 | -1.084744695013 | | 1989 | 0.71262325301468 | | 1988 | 4.624000728883 | | 1987 | 3.5196872187763 | | 1986 | 7.95977476318 | | 1985 | 0.88467649141226 | | 1984 | 1.5568839361552 | | 1983 | 4.8307443601101 | | 1982 | -1.7595853942353 | | 1981 | 3.8247647410283 | | 1980 | 0.35283927106671 | | 1979 | 0.8634217133267 | | 1978 | 1.2943675325915 | | 1977 | -3.9452820470641 | | 1976 | 2.527628304121 | | 1975 | -7.6843535696316 | | 1974 | -3.8054139118098 | | 1973 | 9.9744967452878 | | 1972 | 7.818177129417 |
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