| Year | Value | | 2022 | 1.137688281732 | | 2021 | 1.2149476453304 | | 2020 | 1.2834450921084 | | 2019 | 1.3995144144042 | | 2018 | 1.5484376262019 | | 2017 | 1.5175888785251 | | 2016 | 1.4423513120791 | | 2015 | 1.5373941160003 | | 2014 | 1.8628882627986 | | 2013 | 1.9460776888552 | | 2012 | -5.280077700577 | | 2011 | -4.793553712893 | | 2010 | 2.0510392874164 | | 2009 | 2.0943747020434 | | 2008 | 2.1288784152084 | | 2007 | 2.0514787332128 | | 2006 | 2.2925215495479 | | 2005 | 2.6104013208716 | | 2004 | 2.5810759170562 | | 2003 | 2.5086338172322 | | 2002 | 2.4232450219976 | | 2001 | 2.3225934085193 | | 2000 | 1.8955626656255 | | 1999 | 1.5347707762606 | | 1998 | 1.5909179021523 | | 1997 | 1.6926245135541 | | 1996 | 1.8215059282761 | | 1995 | 1.9578924048939 | | 1994 | 2.0972510635527 | | 1993 | 2.2281753739799 | | 1992 | 2.341098072379 | | 1991 | 2.4476933120465 | | 1990 | 2.5563882950781 | | 1989 | 2.6616446058181 | | 1988 | 2.7637971350614 | | 1987 | 2.9003145322169 | | 1986 | 3.0945936899971 | | 1985 | 3.304709971318 | | 1984 | 4.0346684767635 | | 1983 | 4.7290569995283 | | 1982 | 4.8129295949782 | | 1981 | 4.9162661048574 | | 1980 | 5.0464740815966 | | 1979 | 5.1276161208105 | | 1978 | 5.1492404709478 | | 1977 | 5.1688760890691 | | 1976 | 5.1830272964714 | | 1975 | 5.0284708653888 | | 1974 | 4.4658759026728 | | 1973 | 3.4887156797189 | | 1972 | 2.7437837412314 | | 1971 | 2.5414703681909 | | 1970 | 2.4579180092017 | | 1969 | 2.3590150078175 | | 1968 | 2.2688760348502 | | 1967 | 2.2026186555116 | | 1966 | 2.3117378966092 | | 1965 | 2.8622186572337 | | 1964 | 3.5326415946544 | | 1963 | 3.8089344648408 | | 1962 | 3.7428757183303 | | 1961 | 3.5639371101193 |
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