| Year | Value | | 2022 | 50.058018373558 | | 2021 | 50.062374338763 | | 2020 | 50.067813949112 | | 2019 | 50.075101468638 | | 2018 | 50.083311739711 | | 2017 | 50.093267028048 | | 2016 | 50.106423041741 | | 2015 | 50.121302887964 | | 2014 | 50.134154419718 | | 2013 | 50.145078536235 | | 2012 | 50.156160859653 | | 2011 | 50.166951549116 | | 2010 | 50.178472834529 | | 2009 | 50.189433157328 | | 2008 | 50.199815311505 | | 2007 | 50.210868642051 | | 2006 | 50.221322691668 | | 2005 | 50.230565225915 | | 2004 | 50.239591652203 | | 2003 | 50.249714038287 | | 2002 | 50.261290773388 | | 2001 | 50.270363697207 | | 2000 | 50.276579061212 | | 1999 | 50.280653238878 | | 1998 | 50.279588577411 | | 1997 | 50.278176843081 | | 1996 | 50.27463797982 | | 1995 | 50.271360907414 | | 1994 | 50.2796741478 | | 1993 | 50.289914154884 | | 1992 | 50.29258496137 | | 1991 | 50.293443371144 | | 1990 | 50.29452340123 | | 1989 | 50.296685762647 | | 1988 | 50.291882773675 | | 1987 | 50.286593711649 | | 1986 | 50.288050123915 | | 1985 | 50.289241964165 | | 1984 | 50.286272617614 | | 1983 | 50.279390321517 | | 1982 | 50.272584016073 | | 1981 | 50.263665106843 | | 1980 | 50.255801250532 | | 1979 | 50.253316534545 | | 1978 | 50.254981043706 | | 1977 | 50.259024071036 | | 1976 | 50.266218330591 | | 1975 | 50.276251815415 | | 1974 | 50.28800972165 | | 1973 | 50.298042315275 | | 1972 | 50.303423939013 | | 1971 | 50.307323086889 | | 1970 | 50.311389969546 | | 1969 | 50.314482081623 | | 1968 | 50.318236064216 | | 1967 | 50.321578616614 | | 1966 | 50.326834818097 | | 1965 | 50.334190872036 | | 1964 | 50.340455602744 | | 1963 | 50.34620773464 | | 1962 | 50.352522628984 | | 1961 | 50.35565582175 | | 1960 | 50.35534571805 |
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