| Year | Value | | 2022 | 2.7604145775483 | | 2021 | 2.0430097632988 | | 2020 | 2.1859132836648 | | 2019 | 2.8078168112503 | | 2018 | 2.1494195662191 | | 2017 | 2.0027099025937 | | 2016 | 2.2431638636818 | | 2015 | 2.1313199145947 | | 2014 | 2.2979455909069 | | 2013 | 2.4824131147541 | | 2012 | 2.5271777075949 | | 2008 | 2.7208905265394 | | 2007 | 3.4145952477831 | | 2006 | 3.5117184517902 | | 2005 | 4.4361900410844 | | 2004 | 4.9032668433925 | | 2003 | 5.5334353894983 | | 2002 | 5.4416788594175 | | 2001 | 6.0717371580277 | | 2000 | 4.8624022131156 | | 1999 | 6.2576436568352 | | 1998 | 6.5722725069096 | | 1997 | 6.3596529613228 | | 1996 | 5.8568849187494 | | 1995 | 4.2090728993657 | | 1994 | 3.9211111975145 | | 1993 | 3.7202758201085 | | 1992 | 3.5956379479051 | | 1991 | 3.7862708647433 | | 1990 | 3.4487124725409 | | 1989 | 3.3495221333571 | | 1988 | 3.1452451490121 | | 1987 | 2.6491399122502 | | 1986 | 2.8054131580068 | | 1985 | 2.7511726460413 | | 1984 | 2.9754007853816 | | 1983 | 3.104808925864 | | 1982 | 3.5070248900036 | | 1981 | 3.0303302426868 | | 1980 | 2.9188033688834 | | 1979 | 2.6437153012367 | | 1978 | 2.7963736524325 | | 1977 | 2.5333817419017 | | 1976 | 2.2236011997104 | | 1975 | 2.0568070519099 | | 1974 | 2.2250827510114 | | 1973 | 1.9462122767399 | | 1972 | 1.4586709886548 | | 1971 | 1.0324086542778 | | 1969 | 1.7544913777564 | | 1968 | 1.4142233312539 | | 1967 | 1.3326068841741 | | 1966 | 1.3822879248411 | | 1965 | 1.352337005061 | | 1964 | 0.44562049394079 | | 1963 | 0.43478260869565 | | 1962 | 3.943793911007 |
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