| Year | Value | | 2021 | 62.278229579399 | | 2020 | 62.830384834957 | | 2019 | 63.138905950894 | | 2018 | 62.729662038725 | | 2017 | 62.306834742212 | | 2016 | 61.888234052797 | | 2015 | 61.368895092315 | | 2014 | 60.925259826378 | | 2013 | 60.397258153339 | | 2012 | 59.782559726746 | | 2011 | 59.141748826014 | | 2010 | 58.355593411639 | | 2009 | 57.696470539417 | | 2008 | 56.839127817501 | | 2007 | 56.214903391891 | | 2006 | 55.533828133103 | | 2005 | 54.789105306387 | | 2004 | 54.168607966418 | | 2003 | 53.708367215 | | 2002 | 53.278864426912 | | 2001 | 52.937628603627 | | 2000 | 52.755328922735 | | 1999 | 52.445727340146 | | 1998 | 51.815262932911 | | 1997 | 52.034602161208 | | 1996 | 51.925388436971 | | 1995 | 52.017043317114 | | 1994 | 51.881233992067 | | 1993 | 51.780470674025 | | 1992 | 51.529096618748 | | 1991 | 51.720547455528 | | 1990 | 51.938622160685 | | 1989 | 51.914360953687 | | 1988 | 51.179517247543 | | 1987 | 51.455439863466 | | 1986 | 50.97228872305 | | 1985 | 50.567537037569 | | 1984 | 50.310867921033 | | 1983 | 50.179794277061 | | 1982 | 51.024382330517 | | 1981 | 50.758177719696 | | 1980 | 50.361478168038 | | 1979 | 50.002453502694 | | 1978 | 49.574508006913 | | 1977 | 49.174717480921 | | 1976 | 48.646201207573 | | 1975 | 47.86693997969 | | 1974 | 47.481603716627 | | 1973 | 47.276463372533 | | 1972 | 46.641245129123 | | 1971 | 46.524115885525 | | 1970 | 46.015505914264 | | 1969 | 45.66602412238 | | 1968 | 45.422009657109 | | 1967 | 44.997421050913 | | 1966 | 44.578624746593 | | 1965 | 44.666100376707 | | 1964 | 44.517028320782 | | 1963 | 44.03557896543 | | 1962 | 43.710420673017 | | 1961 | 43.39585564249 | | 1960 | 43.015638094803 |
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