| Year | Value | | 2021 | 71.326865420762 | | 2020 | 72.243465912578 | | 2019 | 72.979143498217 | | 2018 | 72.783210402702 | | 2017 | 72.541695166188 | | 2016 | 72.344348447531 | | 2015 | 72.094340709895 | | 2014 | 71.880875674552 | | 2013 | 71.577225864302 | | 2012 | 71.284377556862 | | 2011 | 71.008297418301 | | 2010 | 70.671200774711 | | 2009 | 70.40149984321 | | 2008 | 70.006100579719 | | 2007 | 69.835114506285 | | 2006 | 69.571229055873 | | 2005 | 69.198741312131 | | 2004 | 68.862305287787 | | 2003 | 68.606836392974 | | 2002 | 68.33322195623 | | 2001 | 68.052240302068 | | 2000 | 67.700401698223 | | 1999 | 67.387195215135 | | 1998 | 67.096779502833 | | 1997 | 66.821740347725 | | 1996 | 66.480034278993 | | 1995 | 66.215657926719 | | 1994 | 66.025234171495 | | 1993 | 65.78025124262 | | 1992 | 65.596375166879 | | 1991 | 65.335190254308 | | 1990 | 65.188406514362 | | 1989 | 65.022815271408 | | 1988 | 64.684862527344 | | 1987 | 64.512756503219 | | 1986 | 64.208231712233 | | 1985 | 63.81228937847 | | 1984 | 63.520124131873 | | 1983 | 63.215640580729 | | 1982 | 62.972214341125 | | 1981 | 62.611283328926 | | 1980 | 62.233555523238 | | 1979 | 61.902752300364 | | 1978 | 61.481454943101 | | 1977 | 61.120866652657 | | 1976 | 60.625810464763 | | 1975 | 60.16610026757 | | 1974 | 59.713633483823 | | 1973 | 59.294651206921 | | 1972 | 58.792924308749 | | 1971 | 57.967237925212 | | 1970 | 57.840946313778 | | 1969 | 57.535551596579 | | 1968 | 57.225421144191 | | 1967 | 56.794784139267 | | 1966 | 56.389743472283 | | 1965 | 55.86063330529 | | 1964 | 56.034875337569 | | 1963 | 55.542340605221 | | 1962 | 55.208683862014 | | 1961 | 52.846336425269 | | 1960 | 50.894179687123 |
|