| Year | Value | | 2022 | 49.011214158187 | | 2021 | 49.006578335704 | | 2020 | 49.009440900728 | | 2019 | 49.018174136751 | | 2018 | 49.032306625295 | | 2017 | 49.060547821288 | | 2016 | 49.09571008653 | | 2015 | 49.129215347685 | | 2014 | 49.167148951897 | | 2013 | 49.225125113567 | | 2012 | 49.300715573217 | | 2011 | 49.365191792581 | | 2010 | 49.411205328298 | | 2009 | 49.451403444617 | | 2008 | 49.461575722757 | | 2007 | 49.411721958966 | | 2006 | 49.349448260063 | | 2005 | 49.289503621967 | | 2004 | 49.200342944938 | | 2003 | 49.114999738339 | | 2002 | 49.033297567088 | | 2001 | 48.985420996938 | | 2000 | 48.982038062228 | | 1999 | 48.977409531868 | | 1998 | 48.973782675774 | | 1997 | 48.969939061798 | | 1996 | 48.968145266209 | | 1995 | 48.967100563907 | | 1994 | 48.964480245106 | | 1993 | 48.959476614048 | | 1992 | 48.954413357539 | | 1991 | 48.951919789447 | | 1990 | 48.966799570963 | | 1989 | 48.994257467144 | | 1988 | 49.015987479875 | | 1987 | 49.032639830541 | | 1986 | 49.044531537147 | | 1985 | 49.054281668292 | | 1984 | 49.061703094906 | | 1983 | 49.064914214813 | | 1982 | 49.064388115586 | | 1981 | 49.059896184315 | | 1980 | 49.05144252592 | | 1979 | 49.039627749791 | | 1978 | 49.022779951403 | | 1977 | 49.002371259704 | | 1976 | 48.981523151789 | | 1975 | 48.958215855955 | | 1974 | 48.903451374342 | | 1973 | 48.849043475002 | | 1972 | 48.824777626765 | | 1971 | 48.804551125573 | | 1970 | 48.782587628534 | | 1969 | 48.762285953094 | | 1968 | 48.746055992444 | | 1967 | 48.727957120059 | | 1966 | 48.709021193467 | | 1965 | 48.686742329935 | | 1964 | 48.66398428381 | | 1963 | 48.641482497091 | | 1962 | 48.616925522894 | | 1961 | 48.592359896891 | | 1960 | 48.561183637694 |
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