| Year | Value | | 2021 | 66.912123928553 | | 2020 | 68.55190231609 | | 2019 | 69.129968177968 | | 2018 | 68.932488306867 | | 2017 | 68.695234813166 | | 2016 | 68.374774333823 | | 2015 | 67.99316574054 | | 2014 | 67.60360316224 | | 2013 | 67.172138921096 | | 2012 | 66.771892972681 | | 2011 | 66.368678811692 | | 2010 | 65.922855374236 | | 2009 | 65.546934164978 | | 2008 | 65.104861545186 | | 2007 | 64.931278879146 | | 2006 | 64.6524048373 | | 2005 | 64.253162840256 | | 2004 | 63.889326152083 | | 2003 | 63.541056944388 | | 2002 | 63.194733815165 | | 2001 | 62.776221664028 | | 2000 | 62.439680427782 | | 1999 | 62.143220690046 | | 1998 | 61.650805987713 | | 1997 | 61.21949228792 | | 1996 | 60.825283987284 | | 1995 | 60.530180567428 | | 1994 | 60.267970534987 | | 1993 | 60.01732825254 | | 1992 | 59.798710213062 | | 1991 | 59.410020570071 | | 1990 | 59.199249541311 | | 1989 | 58.907286578305 | | 1988 | 58.501424776929 | | 1987 | 58.134640336326 | | 1986 | 57.763830905461 | | 1985 | 57.321987591849 | | 1984 | 56.913346817374 | | 1983 | 56.429000688296 | | 1982 | 55.937787489186 | | 1981 | 55.486967765803 | | 1980 | 55.050783329695 | | 1979 | 54.548705578231 | | 1978 | 54.013006721889 | | 1977 | 53.545340623337 | | 1976 | 52.926980775814 | | 1975 | 52.415901555148 | | 1974 | 51.792394830088 | | 1973 | 51.378038498834 | | 1972 | 50.815105336742 | | 1971 | 49.011459099504 | | 1970 | 49.822419068178 | | 1969 | 49.867934573983 | | 1968 | 49.466409416454 | | 1967 | 48.53015806478 | | 1966 | 48.26243778736 | | 1965 | 47.814526014546 | | 1964 | 48.311564948531 | | 1963 | 47.903057764863 | | 1962 | 47.554147910099 | | 1961 | 47.208065142784 | | 1960 | 46.856591636314 |
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