| Year | Value | | 2021 | 72.746055207524 | | 2020 | 72.949768331932 | | 2019 | 73.959115011194 | | 2018 | 73.811517125544 | | 2017 | 73.609742854099 | | 2016 | 73.152521842691 | | 2015 | 72.889516084012 | | 2014 | 72.623863390115 | | 2013 | 72.344242668364 | | 2012 | 72.284678024629 | | 2011 | 72.372285231044 | | 2010 | 72.106383319401 | | 2009 | 71.819806907067 | | 2008 | 71.466391134221 | | 2007 | 71.18035916021 | | 2006 | 70.840288137353 | | 2005 | 70.630930790883 | | 2004 | 70.338439862715 | | 2003 | 69.860181186271 | | 2002 | 69.976592452435 | | 2001 | 69.631131540322 | | 2000 | 69.28217806821 | | 1999 | 68.919395204181 | | 1998 | 68.49643095508 | | 1997 | 68.261594173651 | | 1996 | 67.993667573422 | | 1995 | 67.607456602428 | | 1994 | 67.295436306438 | | 1993 | 67.100899797397 | | 1992 | 66.771982924743 | | 1991 | 66.20223153396 | | 1990 | 65.063272047045 | | 1989 | 65.039940025722 | | 1988 | 64.120678680214 | | 1987 | 63.75486513605 | | 1986 | 63.059201527727 | | 1985 | 62.501823785732 | | 1984 | 61.727615412093 | | 1983 | 60.48971058116 | | 1982 | 59.001418175799 | | 1981 | 58.515326296079 | | 1980 | 58.571006086001 | | 1979 | 58.16529368015 | | 1978 | 56.976034194739 | | 1977 | 56.410653022185 | | 1976 | 55.144926380066 | | 1975 | 54.66199133116 | | 1974 | 54.03670936596 | | 1973 | 53.221513309968 | | 1972 | 52.607349611395 | | 1971 | 52.036007889078 | | 1970 | 51.340929120531 | | 1969 | 50.746792702049 | | 1968 | 50.135277226842 | | 1967 | 49.699264935943 | | 1966 | 49.224965938236 | | 1965 | 48.197518193075 | | 1964 | 47.585561259548 | | 1963 | 46.907868964755 | | 1962 | 46.321542500597 | | 1961 | 46.01085717967 | | 1960 | 44.757572822768 |
|