| Year | Value | | 2021 | 71.792451869362 | | 2020 | 72.207284162998 | | 2019 | 73.111438256296 | | 2018 | 72.87658916354 | | 2017 | 72.435988099552 | | 2016 | 72.32854858774 | | 2015 | 72.203402841862 | | 2014 | 71.988187182348 | | 2013 | 71.71687294009 | | 2012 | 71.429426528242 | | 2011 | 71.143323005945 | | 2010 | 70.836248486291 | | 2009 | 70.582053186714 | | 2008 | 70.170816399853 | | 2007 | 69.941818646096 | | 2006 | 69.672029419031 | | 2005 | 69.290231263769 | | 2004 | 68.849322704535 | | 2003 | 68.676829429774 | | 2002 | 68.442566632345 | | 2001 | 68.144988918455 | | 2000 | 67.814094758734 | | 1999 | 67.55841421775 | | 1998 | 67.325764457337 | | 1997 | 66.989146961724 | | 1996 | 66.578785003345 | | 1995 | 66.189780916832 | | 1994 | 65.855389625586 | | 1993 | 65.563708713312 | | 1992 | 65.463115270736 | | 1991 | 65.181703673383 | | 1990 | 64.859409289524 | | 1989 | 64.681766855831 | | 1988 | 64.409745049585 | | 1987 | 64.217515183279 | | 1986 | 63.912307799915 | | 1985 | 63.42026825472 | | 1984 | 62.998772200286 | | 1983 | 62.633395852196 | | 1982 | 62.216441566936 | | 1981 | 61.751719288069 | | 1980 | 61.315499222107 | | 1979 | 60.89489755125 | | 1978 | 60.427047117458 | | 1977 | 59.930924270568 | | 1976 | 59.407362408279 | | 1975 | 58.806518030844 | | 1974 | 58.318927984268 | | 1973 | 57.821564549566 | | 1972 | 57.138117227752 | | 1971 | 56.510752862157 | | 1970 | 55.714595054617 | | 1969 | 55.048200131784 | | 1968 | 54.589064922766 | | 1967 | 54.087243860821 | | 1966 | 53.402829504634 | | 1965 | 52.341497240323 | | 1964 | 52.559963167295 | | 1963 | 51.923281034838 | | 1962 | 51.384455077904 | | 1961 | 45.724554955242 | | 1960 | 41.484864368838 |
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