| Year | Value | | 2021 | 68.802783019844 | | 2020 | 69.670039034823 | | 2019 | 71.954286796899 | | 2018 | 71.779901012981 | | 2017 | 71.684748782405 | | 2016 | 71.462144881309 | | 2015 | 71.561107203483 | | 2014 | 71.541831409315 | | 2013 | 71.305624240768 | | 2012 | 71.009344956362 | | 2011 | 70.802678298998 | | 2010 | 70.318489174305 | | 2009 | 70.409017870418 | | 2008 | 70.187098592226 | | 2007 | 69.954234747164 | | 2006 | 69.810212718047 | | 2005 | 69.600436482195 | | 2004 | 69.203075641944 | | 2003 | 68.893940876198 | | 2002 | 68.639233515442 | | 2001 | 68.274336297254 | | 2000 | 68.033378550828 | | 1999 | 67.82645112522 | | 1998 | 67.434827462176 | | 1997 | 67.154415595214 | | 1996 | 66.803466642807 | | 1995 | 66.426792407295 | | 1994 | 66.150678472726 | | 1993 | 65.752241163537 | | 1992 | 65.444955964829 | | 1991 | 65.131533057767 | | 1990 | 64.80132520092 | | 1989 | 64.617360362168 | | 1988 | 64.351072027793 | | 1987 | 63.959977157737 | | 1986 | 63.577424001488 | | 1985 | 63.026143115841 | | 1984 | 62.662248967827 | | 1983 | 62.268351346514 | | 1982 | 61.700928014521 | | 1981 | 61.405384886038 | | 1980 | 60.96951728373 | | 1979 | 60.553623113338 | | 1978 | 60.249462232348 | | 1977 | 59.947774136677 | | 1976 | 59.486984800022 | | 1975 | 59.281028165302 | | 1974 | 58.816657724533 | | 1973 | 58.401813578761 | | 1972 | 57.900133537855 | | 1971 | 57.573855223446 | | 1970 | 56.831374668986 | | 1969 | 56.73513881833 | | 1968 | 56.39805457756 | | 1967 | 56.04679447347 | | 1966 | 55.677894995391 | | 1965 | 55.255962916704 | | 1964 | 54.9060386475 | | 1963 | 54.419070954979 | | 1962 | 54.004620102891 | | 1961 | 53.567502650309 | | 1960 | 53.033929595941 |
|