| Year | Value | | 2021 | 35.917662587009 | | 2020 | 35.923716409715 | | 2019 | 35.887974398788 | | 2018 | 35.919071803132 | | 2017 | 35.944684819754 | | 2016 | 35.957448535364 | | 2015 | 35.979916431805 | | 2014 | 35.9591579184 | | 2013 | 36.031468772989 | | 2012 | 36.023295118824 | | 2011 | 36.029770484489 | | 2010 | 36.051027821261 | | 2009 | 35.954044029715 | | 2008 | 35.972178927704 | | 2007 | 36.064823547856 | | 2006 | 36.057535614302 | | 2005 | 36.043911558855 | | 2004 | 36.280115146801 | | 2003 | 36.244542934902 | | 2002 | 36.467676031357 | | 2001 | 36.452302616277 | | 2000 | 36.478765452172 | | 1999 | 36.486863657085 | | 1998 | 36.455131878135 | | 1997 | 36.413164788423 | | 1996 | 36.220422486541 | | 1995 | 36.231518652854 | | 1994 | 36.326057890731 | | 1993 | 36.285537782569 | | 1992 | 36.312702386812 | | 1991 | 40.367809619741 | | 1990 | 40.258867408486 | | 1989 | 40.072858259272 | | 1988 | 39.918527390283 | | 1987 | 39.773444623932 | | 1986 | 39.560605484932 | | 1985 | 39.389101400818 | | 1984 | 39.021365666679 | | 1983 | 38.685599130453 | | 1982 | 38.364029480767 | | 1981 | 38.117093095841 | | 1980 | 38.01705004921 | | 1979 | 37.840426103616 | | 1978 | 37.605470141778 | | 1977 | 37.34117200582 | | 1976 | 37.06150877007 | | 1975 | 37.102036163887 | | 1974 | 36.917033334421 | | 1973 | 36.662812725845 | | 1972 | 36.427301543378 | | 1971 | 36.173342990392 | | 1970 | 35.926328455419 | | 1969 | 35.735955564581 | | 1968 | 35.573815395003 | | 1967 | 35.395689911787 | | 1966 | 35.249517316092 | | 1965 | 35.087914322257 | | 1964 | 34.933053830784 | | 1963 | 34.808495831598 | | 1962 | 34.689224478882 | | 1961 | 34.547063061166 |
|