| Year | Value | | 2022 | 48.546077850087 | | 2021 | 48.594237437934 | | 2020 | 48.645182225939 | | 2019 | 48.695102102698 | | 2018 | 48.745172808799 | | 2017 | 48.794101999935 | | 2016 | 48.842219508517 | | 2015 | 48.88792772488 | | 2014 | 48.930092323084 | | 2013 | 48.970684981569 | | 2012 | 49.009894483168 | | 2011 | 49.048175067585 | | 2010 | 49.086175433722 | | 2009 | 49.115666293399 | | 2008 | 49.136376491297 | | 2007 | 49.156080512305 | | 2006 | 49.174453526318 | | 2005 | 49.191990259697 | | 2004 | 49.20783989678 | | 2003 | 49.22237469757 | | 2002 | 49.236218787847 | | 2001 | 49.249649944418 | | 2000 | 49.26923208469 | | 1999 | 49.311026208673 | | 1998 | 49.373234853155 | | 1997 | 49.445317350764 | | 1996 | 49.523342009918 | | 1995 | 49.595640435445 | | 1994 | 49.675871067075 | | 1993 | 49.766341026724 | | 1992 | 49.854944816402 | | 1991 | 49.928432091592 | | 1990 | 50.001227629041 | | 1989 | 50.051592294265 | | 1988 | 50.06117189607 | | 1987 | 50.068647222219 | | 1986 | 50.075939871593 | | 1985 | 50.084929441561 | | 1984 | 50.095115060373 | | 1983 | 50.105985003461 | | 1982 | 50.118103979972 | | 1981 | 50.133084964564 | | 1980 | 50.149969107577 | | 1979 | 50.165847518049 | | 1978 | 50.178907503108 | | 1977 | 50.188578035161 | | 1976 | 50.195114250164 | | 1975 | 50.199360909871 | | 1974 | 50.20152522141 | | 1973 | 50.201360530918 | | 1972 | 50.19862355893 | | 1971 | 50.193728281384 | | 1970 | 50.187020866944 | | 1969 | 50.178119589395 | | 1968 | 50.166846819762 | | 1967 | 50.154499141746 | | 1966 | 50.142831361702 | | 1965 | 50.131456512823 | | 1964 | 50.119920743858 | | 1963 | 50.109029555552 | | 1962 | 50.099967516665 | | 1961 | 50.093801221556 | | 1960 | 50.089488935872 |
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