| Year | Value | | 2021 | 64.17055579126 | | 2020 | 63.470513364446 | | 2019 | 62.876537971998 | | 2018 | 62.293169282987 | | 2017 | 61.699193890539 | | 2016 | 61.115825201527 | | 2015 | 60.521849809079 | | 2014 | 59.938481120068 | | 2013 | 58.814170555791 | | 2012 | 58.177768349597 | | 2011 | 58.177768349597 | | 2010 | 58.177768349597 | | 2009 | 58.177768349597 | | 2008 | 57.647433177768 | | 2007 | 56.056427662283 | | 2006 | 56.056427662283 | | 2005 | 54.942723801442 | | 2004 | 52.821383114128 | | 2003 | 52.821383114128 | | 2002 | 51.230377598642 | | 2001 | 51.230377598642 | | 2000 | 50.169707254985 | | 1999 | 49.639372083157 | | 1998 | 48.578701739499 | | 1997 | 46.987696224014 | | 1996 | 46.457361052185 | | 1995 | 45.396690708528 | | 1994 | 43.169282986848 | | 1993 | 45.290623674162 | | 1992 | 45.290623674162 | | 1991 | 45.820958845991 | | 1990 | 44.73907509546 | | 1989 | 44.176919813322 | | 1988 | 43.646584641493 | | 1987 | 43.593551124311 | | 1986 | 43.540517607128 | | 1985 | 42.479847263471 | | 1984 | 42.320746711922 | | 1983 | 41.790411540093 | | 1982 | 42.745014849385 | | 1981 | 41.684344505728 | | 1980 | 40.62367416207 | | 1979 | 42.10861264319 | | 1978 | 42.087399236317 | | 1977 | 41.525243954179 | | 1976 | 41.493423843869 | | 1975 | 41.472210436996 | | 1974 | 42.002545608825 | | 1973 | 41.970725498515 | | 1972 | 41.440390326686 | | 1971 | 40.910055154858 | | 1970 | 39.319049639372 | | 1969 | 39.849384811201 | | 1968 | 39.319049639372 | | 1967 | 38.237165888842 | | 1966 | 38.746287653797 | | 1965 | 38.215952481969 | | 1964 | 36.062791684345 | | 1963 | 35.532456512516 | | 1962 | 35.002121340687 | | 1961 | 33.94145099703 |
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