| Year | Value | | 2021 | 70.814483021063 | | 2020 | 70.923359587233 | | 2019 | 71.844626025045 | | 2018 | 71.633016654946 | | 2017 | 71.429596002511 | | 2016 | 70.943062278192 | | 2015 | 70.758222228821 | | 2014 | 70.492628871129 | | 2013 | 70.196513710131 | | 2012 | 70.180460598452 | | 2011 | 70.261519813002 | | 2010 | 70.041253571454 | | 2009 | 69.812637704377 | | 2008 | 69.286427294048 | | 2007 | 68.928680366023 | | 2006 | 68.567249611801 | | 2005 | 68.162682179679 | | 2004 | 67.895912044189 | | 2003 | 67.8590028335 | | 2002 | 67.935570163258 | | 2001 | 67.631680597647 | | 2000 | 67.297331255237 | | 1999 | 66.876727319595 | | 1998 | 65.807706794568 | | 1997 | 65.994419400209 | | 1996 | 65.718404522979 | | 1995 | 65.349783330378 | | 1994 | 65.496726872201 | | 1993 | 64.458321472599 | | 1992 | 63.474410210412 | | 1991 | 63.179614355471 | | 1990 | 62.927967032953 | | 1989 | 62.481143656814 | | 1988 | 60.60902529818 | | 1987 | 61.169711729302 | | 1986 | 61.221262328173 | | 1985 | 60.215736789516 | | 1984 | 59.47897587708 | | 1983 | 58.7873684326 | | 1982 | 58.054797915526 | | 1981 | 57.6929294718 | | 1980 | 57.302372391173 | | 1979 | 56.826292349894 | | 1978 | 56.112173493828 | | 1977 | 55.36147034167 | | 1976 | 54.047533590187 | | 1975 | 53.709858017602 | | 1974 | 53.19444453098 | | 1973 | 52.539683393987 | | 1972 | 51.86445798833 | | 1971 | 51.296423931685 | | 1970 | 50.351343181373 | | 1969 | 49.822235823597 | | 1968 | 49.44511952131 | | 1967 | 48.912911191236 | | 1966 | 48.457072776587 | | 1965 | 48.232107406918 | | 1964 | 47.895758456419 | | 1963 | 46.972471706467 | | 1962 | 46.122575845287 | | 1961 | 45.676401497497 | | 1960 | 44.97289865167 |
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