| Year | Value | | 2021 | 43.102346155392 | | 2020 | 43.029265170699 | | 2019 | 42.59077926254 | | 2018 | 42.37153630846 | | 2017 | 42.986381358502 | | 2016 | 43.47949530272 | | 2015 | 44.118771216323 | | 2014 | 44.283020729421 | | 2013 | 44.921931238102 | | 2012 | 45.581304422496 | | 2011 | 45.791960360874 | | 2010 | 46.138912335705 | | 2009 | 45.430209486643 | | 2008 | 46.423562771085 | | 2007 | 47.491093254991 | | 2006 | 47.553394794442 | | 2005 | 47.473736521126 | | 2004 | 47.318695212099 | | 2003 | 47.1749814557 | | 2002 | 47.031267699301 | | 2001 | 46.993265587261 | | 2000 | 46.958186714608 | | 1999 | 46.922377032108 | | 1998 | 46.892413828384 | | 1997 | 46.857700360655 | | 1996 | 46.823717702772 | | 1995 | 46.788273425196 | | 1994 | 46.75282914762 | | 1993 | 46.71701946512 | | 1992 | 46.682305997391 | | 1991 | 46.647592529662 | | 1990 | 46.612879061933 | | 1989 | 46.578165594203 | | 1988 | 46.545279151091 | | 1987 | 46.546740770785 | | 1986 | 46.546740770785 | | 1985 | 46.546740770785 | | 1984 | 46.546740770785 | | 1983 | 46.547106175709 | | 1982 | 46.546740770785 | | 1981 | 46.546375365862 | | 1980 | 46.546375365862 | | 1979 | 46.546375365862 | | 1978 | 46.546375365862 | | 1977 | 46.546375365862 | | 1976 | 46.546375365862 | | 1975 | 46.546375365862 | | 1974 | 46.546375365862 | | 1973 | 46.546375365862 | | 1972 | 46.546375365862 | | 1971 | 46.546375365862 | | 1970 | 46.546375365862 | | 1969 | 46.546009960938 | | 1968 | 47.223105284121 | | 1967 | 47.394114788303 | | 1966 | 47.849043918018 | | 1965 | 48.153060814341 | | 1964 | 48.707380083239 | | 1963 | 49.283989052468 | | 1962 | 49.853655328152 | | 1961 | 50.363395196387 |
|