| Year | Value | | 2021 | 34.676367939215 | | 2020 | 34.999725855453 | | 2019 | 35.321047293921 | | 2018 | 35.559418303322 | | 2017 | 35.863826528486 | | 2016 | 36.221884373077 | | 2015 | 36.615481362307 | | 2014 | 37.007572806223 | | 2013 | 37.471258921483 | | 2012 | 37.968854788904 | | 2011 | 38.43612928159 | | 2010 | 38.881612690333 | | 2009 | 39.302983140546 | | 2008 | 39.689274384811 | | 2007 | 40.103796144765 | | 2006 | 40.414205969598 | | 2005 | 40.681391840176 | | 2004 | 41.027706112921 | | 2003 | 41.390170702195 | | 2002 | 41.811817689915 | | 2001 | 42.179062165533 | | 2000 | 42.484826788998 | | 1999 | 42.893078525349 | | 1998 | 43.159840285537 | | 1997 | 43.653201044408 | | 1996 | 44.152672501865 | | 1995 | 44.531725503411 | | 1994 | 44.563684316554 | | 1993 | 44.918177997627 | | 1992 | 45.082257857935 | | 1991 | 45.309969978128 | | 1990 | 45.485842470744 | | 1989 | 45.682996248598 | | 1988 | 45.946422180023 | | 1987 | 46.173717401882 | | 1986 | 46.316648428106 | | 1985 | 46.40130578212 | | 1984 | 46.366307520812 | | 1983 | 46.323994940314 | | 1982 | 46.287219587184 | | 1981 | 46.423250347289 | | 1980 | 46.529164385846 | | 1979 | 46.575229035199 | | 1978 | 46.450721888217 | | 1977 | 46.44944959801 | | 1976 | 46.498071856519 | | 1975 | 46.690127253391 | | 1974 | 46.813007371317 | | 1973 | 47.087266630824 | | 1972 | 47.719648688381 | | 1971 | 47.761646705677 | | 1970 | 47.907062530846 | | 1969 | 47.991676201242 | | 1968 | 47.999937917079 | | 1967 | 48.150616587412 | | 1966 | 47.840275684339 | | 1965 | 47.657134656517 | | 1964 | 47.609222336805 | | 1963 | 47.613120921205 | | 1962 | 47.396921438233 | | 1961 | 47.190546083853 | | 1960 | 47.393874380056 |
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