| Year | Value | | 2022 | 50.127916018314 | | 2021 | 50.124814854894 | | 2020 | 50.120835970938 | | 2019 | 50.118858750427 | | 2018 | 50.120802480259 | | 2017 | 50.12424285118 | | 2016 | 50.127360472686 | | 2015 | 50.131985662122 | | 2014 | 50.137638343221 | | 2013 | 50.14493600266 | | 2012 | 50.152400918553 | | 2011 | 50.160549472351 | | 2010 | 50.174475035288 | | 2009 | 50.189180594965 | | 2008 | 50.204515013039 | | 2007 | 50.22099414889 | | 2006 | 50.238599020737 | | 2005 | 50.258152760345 | | 2004 | 50.277630636903 | | 2003 | 50.298004914692 | | 2002 | 50.320035440237 | | 2001 | 50.345538530541 | | 2000 | 50.371340634986 | | 1999 | 50.388430473065 | | 1998 | 50.398200174964 | | 1997 | 50.407783210459 | | 1996 | 50.409084056779 | | 1995 | 50.400146247974 | | 1994 | 50.386007649617 | | 1993 | 50.391720365379 | | 1992 | 50.418075912468 | | 1991 | 50.441175421724 | | 1990 | 50.463365594651 | | 1989 | 50.482383362652 | | 1988 | 50.497635682683 | | 1987 | 50.510628693454 | | 1986 | 50.520574401851 | | 1985 | 50.527032197256 | | 1984 | 50.533030311366 | | 1983 | 50.47617741996 | | 1982 | 50.375471514606 | | 1981 | 50.315337150044 | | 1980 | 50.262143743164 | | 1979 | 50.186480601441 | | 1978 | 50.103805081504 | | 1977 | 50.023915763305 | | 1976 | 50.000456751095 | | 1975 | 50.016151072964 | | 1974 | 50.003372322897 | | 1973 | 49.980839864537 | | 1972 | 49.962662631626 | | 1971 | 49.969436411378 | | 1970 | 49.959111454153 | | 1969 | 49.899436317296 | | 1968 | 49.819996122664 | | 1967 | 49.728082203619 | | 1966 | 49.628300857717 | | 1965 | 49.521163617633 | | 1964 | 49.40276401286 | | 1963 | 49.275399045057 | | 1962 | 49.141802605947 | | 1961 | 49.000292445002 | | 1960 | 48.885829579933 |
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