| Year | Value | | 2022 | 1.8971149690147 | | 2021 | 2.0220361672957 | | 2020 | 1.8659944984362 | | 2019 | 1.5284032671987 | | 2018 | 1.5775996033196 | | 2017 | 1.6497897623371 | | 2016 | 1.7291610757073 | | 2015 | 1.8198238915477 | | 2014 | 1.9118597739315 | | 2013 | 1.998080447393 | | 2012 | 2.0640787261862 | | 2011 | 2.12185633623 | | 2010 | 2.2262248528633 | | 2009 | 2.3424105530307 | | 2008 | 2.4192031021932 | | 2007 | 2.4556468306657 | | 2006 | 2.471071503209 | | 2005 | 2.4943602769591 | | 2004 | 2.5269517904307 | | 2003 | 2.5831220522533 | | 2002 | 2.4202546428305 | | 2001 | 1.7546971939805 | | 2000 | 1.3351183534782 | | 1999 | 1.4332733513005 | | 1998 | 1.5383477032181 | | 1997 | 1.6435836607293 | | 1996 | 1.7394074778761 | | 1995 | 1.8283458996282 | | 1994 | 1.9193320055967 | | 1993 | 1.9966782380035 | | 1992 | 2.0617297519244 | | 1991 | 2.2521050265006 | | 1990 | 2.4375859956469 | | 1989 | 2.5281785224451 | | 1988 | 2.5677701999724 | | 1987 | 2.3974744703207 | | 1986 | 2.1886731347317 | | 1985 | 1.9990812758292 | | 1984 | 1.7833219393866 | | 1983 | 1.6888028406327 | | 1982 | 1.7601565860582 | | 1981 | 1.9961962365056 | | 1980 | 2.2817763873186 | | 1979 | 2.5129735172844 | | 1978 | 2.5799701622447 | | 1977 | 2.4903600638211 | | 1976 | 2.3445349238132 | | 1975 | 2.1713164904364 | | 1974 | 2.0605429589709 | | 1973 | 2.0048801740514 | | 1972 | 2.0105512277924 | | 1971 | 2.0956196751233 | | 1970 | 1.9838976125848 | | 1969 | 1.7507310647086 | | 1968 | 1.5846268614744 | | 1967 | 1.364550259763 | | 1966 | 1.1601202900761 | | 1965 | 1.0341875501789 | | 1964 | 1.0193768189543 | | 1963 | 1.0758945489874 | | 1962 | 1.1792504173399 | | 1961 | 0.97556041619417 |
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