| Year | Value | | 2021 | 64.210490485769 | | 2020 | 64.629721543421 | | 2019 | 65.151004989792 | | 2018 | 64.813797534886 | | 2017 | 64.40959625491 | | 2016 | 64.014522154614 | | 2015 | 63.490432581037 | | 2014 | 63.117908891942 | | 2013 | 62.698315149659 | | 2012 | 62.254889026279 | | 2011 | 61.680115018665 | | 2010 | 60.960056099484 | | 2009 | 60.499388791602 | | 2008 | 59.507040618005 | | 2007 | 59.367779156409 | | 2006 | 58.938554191481 | | 2005 | 58.340116794753 | | 2004 | 57.803997095258 | | 2003 | 57.32430016746 | | 2002 | 56.74169501158 | | 2001 | 56.267214469492 | | 2000 | 55.787282292298 | | 1999 | 55.197995509642 | | 1998 | 53.953939505291 | | 1997 | 53.654579359859 | | 1996 | 52.947805607476 | | 1995 | 52.799804574527 | | 1994 | 52.292665730952 | | 1993 | 51.613214740848 | | 1992 | 51.067469415541 | | 1991 | 50.413919665049 | | 1990 | 50.696675670162 | | 1989 | 50.441953382952 | | 1988 | 49.441232434132 | | 1987 | 49.626441242518 | | 1986 | 49.060653443834 | | 1985 | 48.417560303255 | | 1984 | 48.04759896141 | | 1983 | 47.979076931048 | | 1982 | 48.706634808747 | | 1981 | 48.419851777892 | | 1980 | 48.087291729203 | | 1979 | 47.623724844801 | | 1978 | 47.136690612266 | | 1977 | 46.817741164035 | | 1976 | 46.100214234501 | | 1975 | 45.481000411095 | | 1974 | 45.566884635284 | | 1973 | 45.629249884236 | | 1972 | 45.046828804651 | | 1971 | 40.057364765907 | | 1970 | 43.243406756066 | | 1969 | 44.565890275963 | | 1968 | 44.323763839755 | | 1967 | 43.961404628979 | | 1966 | 43.362287267136 | | 1965 | 42.97901127024 | | 1964 | 43.008273026769 | | 1963 | 42.281542495751 | | 1962 | 42.158082394468 | | 1961 | 41.658317775399 | | 1960 | 41.228513615443 |
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