| Year | Value | | 2022 | 47.941808822837 | | 2021 | 47.915287541111 | | 2020 | 47.870969105279 | | 2019 | 48.287219002936 | | 2018 | 47.570944446249 | | 2017 | 46.241342319442 | | 2016 | 46.209711899449 | | 2015 | 46.155615313849 | | 2014 | 46.06993006993 | | 2013 | 45.949101940579 | | 2012 | 45.79073852685 | | 2011 | 45.743674115675 | | 2010 | 45.82318986071 | | 2009 | 45.893892108783 | | 2008 | 45.961173966763 | | 2007 | 46.029753022305 | | 2006 | 46.099262347659 | | 2005 | 46.165024480012 | | 2004 | 46.218371552835 | | 2003 | 46.260167146491 | | 2002 | 46.281704884639 | | 2001 | 46.301313366185 | | 2000 | 46.391701549949 | | 1999 | 46.549762305324 | | 1998 | 46.715318416523 | | 1997 | 46.87553093887 | | 1996 | 47.03030791336 | | 1995 | 47.173156608585 | | 1994 | 47.307168828778 | | 1993 | 47.433615625835 | | 1992 | 47.544955174379 | | 1991 | 47.643867605034 | | 1990 | 47.733618105323 | | 1989 | 47.817015785791 | | 1988 | 47.900899111142 | | 1987 | 47.986714620317 | | 1986 | 48.068491224482 | | 1985 | 48.143821142883 | | 1984 | 48.221369080265 | | 1983 | 48.298292558614 | | 1982 | 48.372472110438 | | 1981 | 48.451192174445 | | 1980 | 48.534596527915 | | 1979 | 48.611501417878 | | 1978 | 48.687082013376 | | 1977 | 48.759901228233 | | 1976 | 48.82931533269 | | 1975 | 48.899459236486 | | 1974 | 48.969222116634 | | 1973 | 49.032421347731 | | 1972 | 49.106274676151 | | 1971 | 49.178105628891 | | 1970 | 49.232303753699 | | 1969 | 49.28262492685 | | 1968 | 49.328230655562 | | 1967 | 49.373262415751 | | 1966 | 49.420336470555 | | 1965 | 49.46649745833 | | 1964 | 49.513222795841 | | 1963 | 49.563415932948 | | 1962 | 49.613975350679 | | 1961 | 49.66945128914 | | 1960 | 49.740999741 |
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