| Year | Value | | 2022 | 48.325272362965 | | 2021 | 48.341132735229 | | 2020 | 48.350110692372 | | 2019 | 48.356160773831 | | 2018 | 48.359908290588 | | 2017 | 48.362502195448 | | 2016 | 48.36553425424 | | 2015 | 48.369770779142 | | 2014 | 48.375019624227 | | 2013 | 48.381073520277 | | 2012 | 48.386402169883 | | 2011 | 48.393920038701 | | 2010 | 48.403722616893 | | 2009 | 48.413021914636 | | 2008 | 48.422602747794 | | 2007 | 48.434055484276 | | 2006 | 48.446353896927 | | 2005 | 48.458188263149 | | 2004 | 48.470663969009 | | 2003 | 48.480059573808 | | 2002 | 48.487344016499 | | 2001 | 48.496923787149 | | 2000 | 48.506237563699 | | 1999 | 48.514448673476 | | 1998 | 48.523937805878 | | 1997 | 48.535252713623 | | 1996 | 48.548462564838 | | 1995 | 48.564327903656 | | 1994 | 48.583142444448 | | 1993 | 48.602773259425 | | 1992 | 48.621478724132 | | 1991 | 48.640097844099 | | 1990 | 48.658178288557 | | 1989 | 48.676639330341 | | 1988 | 48.695849177874 | | 1987 | 48.716326889652 | | 1986 | 48.736388316048 | | 1985 | 48.75485105585 | | 1984 | 48.773795271777 | | 1983 | 48.79088892609 | | 1982 | 48.805288605894 | | 1981 | 48.817238149597 | | 1980 | 48.828169579417 | | 1979 | 48.840865375536 | | 1978 | 48.853784751867 | | 1977 | 48.864668905363 | | 1976 | 48.872559550141 | | 1975 | 48.876624093447 | | 1974 | 48.874415223871 | | 1973 | 48.864074095697 | | 1972 | 48.849052087028 | | 1971 | 48.830716424562 | | 1970 | 48.808008204327 | | 1969 | 48.786699332197 | | 1968 | 48.765786338462 | | 1967 | 48.741176798306 | | 1966 | 48.714000998211 | | 1965 | 48.684690199076 | | 1964 | 48.65336751945 | | 1963 | 48.619192951324 | | 1962 | 48.582552115314 | | 1961 | 48.54512371641 | | 1960 | 48.505712109673 |
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