| Year | Value | | 2021 | 68.178741366416 | | 2020 | 69.254795591678 | | 2019 | 70.044559085184 | | 2018 | 69.86003110079 | | 2017 | 69.534347142371 | | 2016 | 69.335196361439 | | 2015 | 69.070368538201 | | 2014 | 68.75233685151 | | 2013 | 68.383148150026 | | 2012 | 68.0517059372 | | 2011 | 67.724754422623 | | 2010 | 67.375020740807 | | 2009 | 67.083007830998 | | 2008 | 66.693319646827 | | 2007 | 66.51363506658 | | 2006 | 66.279418054479 | | 2005 | 65.937819925052 | | 2004 | 65.578191642039 | | 2003 | 65.356633055556 | | 2002 | 65.105932357937 | | 2001 | 64.786707082229 | | 2000 | 64.487531799659 | | 1999 | 64.245433700332 | | 1998 | 63.917725930012 | | 1997 | 63.552485575698 | | 1996 | 63.186841536101 | | 1995 | 62.851165680907 | | 1994 | 62.558815601322 | | 1993 | 62.299388019546 | | 1992 | 62.143347421645 | | 1991 | 61.833653783208 | | 1990 | 61.584605187256 | | 1989 | 61.376756949463 | | 1988 | 61.050056081723 | | 1987 | 60.811381927398 | | 1986 | 60.497804703754 | | 1985 | 60.046906372283 | | 1984 | 59.649575664889 | | 1983 | 59.249816990754 | | 1982 | 58.837976449267 | | 1981 | 58.43113613416 | | 1980 | 58.064891584226 | | 1979 | 57.657982766481 | | 1978 | 57.21515430193 | | 1977 | 56.793660835461 | | 1976 | 56.294111596984 | | 1975 | 55.757396061686 | | 1974 | 55.214792222208 | | 1973 | 54.763190304958 | | 1972 | 54.136130317748 | | 1971 | 52.818684967016 | | 1970 | 52.905651818257 | | 1969 | 52.528817089856 | | 1968 | 52.093003933417 | | 1967 | 51.399700915492 | | 1966 | 50.926844259584 | | 1965 | 50.141046842054 | | 1964 | 50.503153637244 | | 1963 | 49.973952298529 | | 1962 | 49.517650210281 | | 1961 | 46.185847499836 | | 1960 | 43.632647117525 |
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