| Year | Value | | 2021 | 68.719688651914 | | 2020 | 69.549268997329 | | 2019 | 71.880073520446 | | 2018 | 71.699558231304 | | 2017 | 71.599313016241 | | 2016 | 71.362271138106 | | 2015 | 71.461175979954 | | 2014 | 71.44108161653 | | 2013 | 71.197589512192 | | 2012 | 70.894875571499 | | 2011 | 70.684133930317 | | 2010 | 70.189460001834 | | 2009 | 70.285360402032 | | 2008 | 70.058742220129 | | 2007 | 69.821853125223 | | 2006 | 69.675600529846 | | 2005 | 69.462766509796 | | 2004 | 69.055597189653 | | 2003 | 68.740397490368 | | 2002 | 68.48093073309 | | 2001 | 68.109485678973 | | 2000 | 67.868314036946 | | 1999 | 67.664265007449 | | 1998 | 67.268864402419 | | 1997 | 66.988143920375 | | 1996 | 66.634228587495 | | 1995 | 66.251671573294 | | 1994 | 65.971465324964 | | 1993 | 65.560912862718 | | 1992 | 65.239867834328 | | 1991 | 64.914932118591 | | 1990 | 64.570302696372 | | 1989 | 64.378277142002 | | 1988 | 64.10068284201 | | 1987 | 63.694171443552 | | 1986 | 63.295930878775 | | 1985 | 62.728575912737 | | 1984 | 62.346567348876 | | 1983 | 61.938596181897 | | 1982 | 61.349586416541 | | 1981 | 61.045630439979 | | 1980 | 60.594002472651 | | 1979 | 60.164355193711 | | 1978 | 59.849657257453 | | 1977 | 59.537559924155 | | 1976 | 59.065181538957 | | 1975 | 58.862001344594 | | 1974 | 58.392314834634 | | 1973 | 57.973673253592 | | 1972 | 57.466021041632 | | 1971 | 57.138997164951 | | 1970 | 56.377512598323 | | 1969 | 56.288237129188 | | 1968 | 55.947639562473 | | 1967 | 55.591633746502 | | 1966 | 55.217598553183 | | 1965 | 54.787351350202 | | 1964 | 54.432981942362 | | 1963 | 53.949596914227 | | 1962 | 53.513551726835 | | 1961 | 53.071878380101 | | 1960 | 52.519297025523 |
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