| Year | Value | | 2021 | 42.058380100545 | | 2020 | 42.040812264747 | | 2019 | 42.003206797431 | | 2018 | 42.017214319394 | | 2017 | 41.954448800237 | | 2016 | 41.893289744046 | | 2015 | 41.833362467623 | | 2014 | 41.70128218242 | | 2013 | 41.684811872253 | | 2012 | 41.580272504025 | | 2011 | 41.548912622193 | | 2010 | 41.454013353446 | | 2009 | 41.410707663671 | | 2008 | 41.317488915247 | | 2007 | 41.295926221536 | | 2006 | 41.224196385742 | | 2005 | 41.139577163926 | | 2004 | 41.781543583931 | | 2003 | 41.729361807674 | | 2002 | 42.377229315263 | | 2001 | 42.335874148684 | | 2000 | 42.262792693791 | | 1999 | 42.259014336677 | | 1998 | 42.146641610749 | | 1997 | 42.064371494994 | | 1996 | 41.53273248038 | | 1995 | 41.455033359046 | | 1994 | 41.279506293698 | | 1993 | 41.138969150844 | | 1992 | 41.205568472251 | | 1991 | 39.861398732463 | | 1990 | 39.688263161308 | | 1989 | 39.717900674507 | | 1988 | 39.594290891844 | | 1987 | 39.531158901619 | | 1986 | 39.376576129828 | | 1985 | 39.384864986705 | | 1984 | 39.261368073583 | | 1983 | 39.079382693673 | | 1982 | 39.110527632492 | | 1981 | 38.940591076026 | | 1980 | 39.051935114097 | | 1979 | 39.059540581179 | | 1978 | 39.033461544781 | | 1977 | 38.929850833817 | | 1976 | 38.853487535354 | | 1975 | 39.484366540961 | | 1974 | 39.412818351606 | | 1973 | 39.359488670364 | | 1972 | 39.269248439619 | | 1971 | 39.157614049614 | | 1970 | 39.053452814864 | | 1969 | 38.940385518984 | | 1968 | 38.990294732841 | | 1967 | 38.940297340161 | | 1966 | 38.88368653575 | | 1965 | 38.810806738484 | | 1964 | 38.692867562629 | | 1963 | 38.596532198427 | | 1962 | 38.533572518755 | | 1961 | 38.450993050951 |
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