| Year | Value | | 2022 | 9.0896391152503 | | 2021 | 4.4808796341344 | | 2020 | 3.4684117795118 | | 2019 | 4.3658715981927 | | 2018 | 4.3473493777753 | | 2017 | 3.9343608444204 | | 2016 | 2.7246122329529 | | 2015 | 3.1578311798092 | | 2014 | 6.1292493031302 | | 2013 | 5.1618989858149 | | 2012 | 5.1961861553185 | | 2011 | 6.7622795731476 | | 2010 | 4.6988906497623 | | 2009 | 5.4963427377221 | | 2008 | 11.403427081393 | | 2007 | 6.9362147089577 | | 2006 | 5.577752076543 | | 2005 | 8.8090607481982 | | 2004 | 8.1137909709338 | | 2003 | 7.6741663939794 | | 2002 | 7.6905097203427 | | 2001 | 9.6741555686538 | | 2000 | 11.048034934498 | | 1999 | 11.66374097913 | | 1998 | 13.668107748587 | | 1997 | 20.199866755496 | | 1996 | 23.837835307336 | | 1995 | 29.464529228159 | | 1994 | 21.729346883819 | | 1993 | 10.748646716372 | | 1992 | 8.7598862525549 | | 1991 | 33.972260253586 | | 1990 | 23.322566436647 | | 1989 | 9.850409257691 | | 1988 | 4.4912576364018 | | 1987 | 2.487154022239 | | 1986 | 4.3527238320756 | | 1985 | 3.3626752360861 | | 1984 | 4.7263681592039 | | 1983 | 8.2528116584826 | | 1982 | 8.9826217061689 | | 1981 | 9.405691261425 | | 1980 | 18.061543035596 | | 1979 | 12.135355892606 | | 1978 | 5.7483246461823 | | 1977 | 8.4347077189513 | | 1976 | 4.883418957909 | | 1975 | 8.3761625062971 | | 1974 | 12.849547745419 | | 1973 | 5.1932016269113 | | 1972 | 3.6122817579933 | | 1971 | 2.2232479422376 | | 1970 | 2.8808864266098 | | 1969 | 1.258214457371 | | 1968 | 1.8612244897209 | | 1967 | 2.0918409866731 | | 1966 | 1.7842346571874 | | 1965 | 3.1862745099876 | | 1964 | 4.4721014708073 | | 1963 | 3.0814560186727 | | 1962 | 1.0921501708401 | | 1961 | 1.5629923739269 | | 1960 | -1.7462381571075 |
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