| Year | Value | | 2022 | 50.488111601229 | | 2021 | 50.501350168729 | | 2020 | 50.514717643557 | | 2019 | 50.525960431693 | | 2018 | 50.535145539858 | | 2017 | 50.543916686282 | | 2016 | 50.552131014741 | | 2015 | 50.559884576962 | | 2014 | 50.5662672223 | | 2013 | 50.572206926345 | | 2012 | 50.577927422729 | | 2011 | 50.581594395317 | | 2010 | 50.582971134666 | | 2009 | 50.581820018165 | | 2008 | 50.578768090013 | | 2007 | 50.574562664317 | | 2006 | 50.569875535816 | | 2005 | 50.564926454268 | | 2004 | 50.561048578251 | | 2003 | 50.556833693864 | | 2002 | 50.550577016109 | | 2001 | 50.545879771467 | | 2000 | 50.542256139468 | | 1999 | 50.538127772636 | | 1998 | 50.525803367722 | | 1997 | 50.513239341991 | | 1996 | 50.510344596799 | | 1995 | 50.508822549835 | | 1994 | 50.508320104215 | | 1993 | 50.509028731229 | | 1992 | 50.510348987628 | | 1991 | 50.51168131999 | | 1990 | 50.512938842729 | | 1989 | 50.514930166336 | | 1988 | 50.51781937392 | | 1987 | 50.514267608578 | | 1986 | 50.502572433855 | | 1985 | 50.487944347975 | | 1984 | 50.473038084487 | | 1983 | 50.458772135036 | | 1982 | 50.443104187196 | | 1981 | 50.424618095271 | | 1980 | 50.40360085654 | | 1979 | 50.381299662329 | | 1978 | 50.357061577842 | | 1977 | 50.33154883785 | | 1976 | 50.304934548074 | | 1975 | 50.276810687854 | | 1974 | 50.245764519427 | | 1973 | 50.220089506239 | | 1972 | 50.204853077837 | | 1971 | 50.19213593997 | | 1970 | 50.17969614982 | | 1969 | 50.168117714606 | | 1968 | 50.156844385512 | | 1967 | 50.146634127538 | | 1966 | 50.137945777833 | | 1965 | 50.13029105895 | | 1964 | 50.125080745618 | | 1963 | 50.119900798516 | | 1962 | 50.113489137274 | | 1961 | 50.108835437454 | | 1960 | 50.106777727691 |
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