| Year | Value | | 2021 | 10.339925035543 | | 2020 | 10.339925035543 | | 2019 | 10.339925035543 | | 2018 | 10.339925035543 | | 2017 | 10.339925035543 | | 2016 | 10.339925035543 | | 2015 | 10.339925035543 | | 2014 | 10.339925035543 | | 2013 | 10.339925035543 | | 2012 | 10.339925035543 | | 2011 | 10.856921287321 | | 2010 | 10.339925035543 | | 2009 | 10.598423161432 | | 2008 | 10.986170350265 | | 2007 | 10.339925035543 | | 2006 | 10.598423161432 | | 2005 | 10.081426909655 | | 2004 | 9.8229287837663 | | 2003 | 9.4351815949334 | | 2002 | 9.4351815949334 | | 2001 | 9.3059325319891 | | 2000 | 9.3059325319891 | | 1999 | 9.1766834690448 | | 1998 | 8.788936280212 | | 1997 | 9.0474344061006 | | 1996 | 8.788936280212 | | 1995 | 8.0392917151351 | | 1994 | 8.0134419025462 | | 1993 | 7.8324932144242 | | 1992 | 7.7290939640688 | | 1991 | 7.6256947137133 | | 1990 | 7.5222954633579 | | 1989 | 7.4188962130025 | | 1988 | 7.315496962647 | | 1987 | 7.2120977122916 | | 1986 | 7.0957735556417 | | 1985 | 6.9923743052863 | | 1984 | 6.8889750549309 | | 1983 | 6.7855758045754 | | 1982 | 6.68217655422 | | 1981 | 6.5787773038646 | | 1980 | 6.4753780535091 | | 1979 | 6.3719788031537 | | 1978 | 6.3719788031537 | | 1977 | 6.3719788031537 | | 1976 | 6.3719788031537 | | 1975 | 6.3719788031537 | | 1974 | 6.3719788031537 | | 1973 | 6.2427297402094 | | 1972 | 6.2427297402094 | | 1971 | 6.1651803024428 | | 1970 | 6.0359312394985 | | 1969 | 5.9066821765542 | | 1968 | 5.7774331136099 | | 1967 | 5.6481840506656 | | 1966 | 5.5189349877213 | | 1965 | 5.3379862995993 | | 1964 | 5.2604368618328 | | 1963 | 5.1311877988885 | | 1962 | 5.0019387359442 | | 1961 | 4.8726896729999 |
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