| Year | Value | | 2021 | 65.976042243444 | | 2020 | 67.142638198189 | | 2019 | 67.682845022856 | | 2018 | 67.522612127826 | | 2017 | 67.385488570069 | | 2016 | 67.054128815058 | | 2015 | 66.620835880376 | | 2014 | 66.191011557344 | | 2013 | 65.869694736559 | | 2012 | 65.443219291279 | | 2011 | 64.940748698565 | | 2010 | 64.523485410614 | | 2009 | 63.947595859152 | | 2008 | 63.38258735865 | | 2007 | 62.794228212131 | | 2006 | 62.174320751775 | | 2005 | 61.634370310865 | | 2004 | 61.306961089876 | | 2003 | 61.063651518229 | | 2002 | 60.912943600372 | | 2001 | 60.885452728103 | | 2000 | 60.884691758405 | | 1999 | 60.353877396708 | | 1998 | 60.571323906506 | | 1997 | 60.859821185598 | | 1996 | 61.120628142671 | | 1995 | 61.181093859193 | | 1994 | 61.314259451569 | | 1993 | 61.55479848333 | | 1992 | 61.519558090138 | | 1991 | 61.602321508297 | | 1990 | 61.664292787665 | | 1989 | 61.664280683791 | | 1988 | 61.032410980198 | | 1987 | 60.850764920409 | | 1986 | 60.507105057216 | | 1985 | 60.194229026636 | | 1984 | 59.900102644225 | | 1983 | 59.546404633154 | | 1982 | 59.287663754776 | | 1981 | 58.908609142136 | | 1980 | 58.574150899573 | | 1979 | 58.17761008609 | | 1978 | 57.854252620501 | | 1977 | 57.640398033951 | | 1976 | 57.167744768439 | | 1975 | 56.981047146488 | | 1974 | 56.562292741419 | | 1973 | 56.934902150053 | | 1972 | 56.594800213121 | | 1971 | 56.145866269924 | | 1970 | 55.747930808692 | | 1969 | 55.402654934052 | | 1968 | 55.499110281527 | | 1967 | 55.283692542472 | | 1966 | 55.025811620719 | | 1965 | 54.728469887886 | | 1964 | 54.172428826699 | | 1963 | 53.653485345465 | | 1962 | 53.572742007139 | | 1961 | 53.133332706851 | | 1960 | 52.71666258763 |
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