| Year | Value | | 2021 | 68.946382428187 | | 2020 | 70.583781828625 | | 2019 | 71.048686274805 | | 2018 | 70.806729841212 | | 2017 | 70.579722849689 | | 2016 | 70.239573807938 | | 2015 | 69.896725526519 | | 2014 | 69.561632597492 | | 2013 | 69.201124374529 | | 2012 | 68.789614762401 | | 2011 | 68.367784353609 | | 2010 | 67.893624528289 | | 2009 | 67.499209946368 | | 2008 | 67.010775747384 | | 2007 | 66.821021051197 | | 2006 | 66.488153445453 | | 2005 | 66.012672419935 | | 2004 | 65.587368844333 | | 2003 | 65.190697822071 | | 2002 | 64.790597324161 | | 2001 | 64.324458481027 | | 2000 | 63.948093470292 | | 1999 | 63.615579438542 | | 1998 | 63.08979318451 | | 1997 | 62.658484775097 | | 1996 | 62.223177758552 | | 1995 | 61.943531539819 | | 1994 | 61.703539716773 | | 1993 | 61.467337536356 | | 1992 | 61.282633504487 | | 1991 | 60.882182967577 | | 1990 | 60.665866429062 | | 1989 | 60.350014820387 | | 1988 | 59.957076495226 | | 1987 | 59.536764330199 | | 1986 | 59.146286290665 | | 1985 | 58.697027003798 | | 1984 | 58.291614547898 | | 1983 | 57.807150613938 | | 1982 | 57.261275828165 | | 1981 | 56.719510953585 | | 1980 | 56.149788241653 | | 1979 | 55.57631153367 | | 1978 | 54.939556596527 | | 1977 | 54.340245755133 | | 1976 | 53.602686228859 | | 1975 | 53.074339542841 | | 1974 | 52.468378765783 | | 1973 | 52.040737517119 | | 1972 | 51.488389595112 | | 1971 | 50.22556884962 | | 1970 | 50.47505006996 | | 1969 | 50.548501022976 | | 1968 | 50.151539469925 | | 1967 | 49.194118759441 | | 1966 | 48.846909293638 | | 1965 | 48.380370013873 | | 1964 | 48.826539941496 | | 1963 | 48.405242162363 | | 1962 | 48.057152042057 | | 1961 | 47.746425141954 | | 1960 | 47.380389554536 |
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