| Year | Value | | 2022 | 50.696697445334 | | 2021 | 50.665882944596 | | 2020 | 50.639583282856 | | 2019 | 50.62645796039 | | 2018 | 50.623874715001 | | 2017 | 50.623069469512 | | 2016 | 50.619434297958 | | 2015 | 50.61012873419 | | 2014 | 50.596413334117 | | 2013 | 50.58086294088 | | 2012 | 50.565257400019 | | 2011 | 50.55011599377 | | 2010 | 50.53579172917 | | 2009 | 50.521264008325 | | 2008 | 50.504466326647 | | 2007 | 50.485785278552 | | 2006 | 50.46722329624 | | 2005 | 50.450207882629 | | 2004 | 50.433741926555 | | 2003 | 50.416157149817 | | 2002 | 50.396699465196 | | 2001 | 50.374752669413 | | 2000 | 50.351097860558 | | 1999 | 50.32616921696 | | 1998 | 50.300073154378 | | 1997 | 50.273278846859 | | 1996 | 50.246006470798 | | 1995 | 50.218096412907 | | 1994 | 50.189088052994 | | 1993 | 50.158367527586 | | 1992 | 50.125623769135 | | 1991 | 50.091850274045 | | 1990 | 50.058655469108 | | 1989 | 50.027232616414 | | 1988 | 49.998673885465 | | 1987 | 49.974669189814 | | 1986 | 49.956400347248 | | 1985 | 49.944950361894 | | 1984 | 49.937530133467 | | 1983 | 49.931469672152 | | 1982 | 49.92801364588 | | 1981 | 49.926312203152 | | 1980 | 49.925862028458 | | 1979 | 49.927122778034 | | 1978 | 49.930210072082 | | 1977 | 49.935067713754 | | 1976 | 49.941956262957 | | 1975 | 49.950604029759 | | 1974 | 49.960614242259 | | 1973 | 49.971464059405 | | 1972 | 49.983270203678 | | 1971 | 49.996671402696 | | 1970 | 50.011470800594 | | 1969 | 50.027466298004 | | 1968 | 50.044848401834 | | 1967 | 50.063676203648 | | 1966 | 50.083616818242 | | 1965 | 50.104006311292 | | 1964 | 50.124483124174 | | 1963 | 50.145058763732 | | 1962 | 50.165277897767 | | 1961 | 50.184799375421 | | 1960 | 50.203764888746 |
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