| Year | Value | | 2022 | 49.355084611128 | | 2021 | 49.393057753007 | | 2020 | 49.440593244888 | | 2019 | 49.486003933502 | | 2018 | 49.523864034323 | | 2017 | 49.560227315155 | | 2016 | 49.595885284084 | | 2015 | 49.630850356284 | | 2014 | 49.664422307285 | | 2013 | 49.697724411174 | | 2012 | 49.730835250591 | | 2011 | 49.749767233766 | | 2010 | 49.767211075328 | | 2009 | 49.797236850207 | | 2008 | 49.826017426346 | | 2007 | 49.854754950075 | | 2006 | 49.884552553627 | | 2005 | 49.914028645952 | | 2004 | 49.956807201553 | | 2003 | 50.008858327387 | | 2002 | 50.054658147095 | | 2001 | 50.097812703255 | | 2000 | 50.139488115006 | | 1999 | 50.181144039983 | | 1998 | 50.222338234364 | | 1997 | 50.260359231919 | | 1996 | 50.294023148173 | | 1995 | 50.322720796479 | | 1994 | 50.336290340486 | | 1993 | 50.339154653698 | | 1992 | 50.343355440589 | | 1991 | 50.347837310923 | | 1990 | 50.352481266935 | | 1989 | 50.356148130492 | | 1988 | 50.359050206797 | | 1987 | 50.363575082592 | | 1986 | 50.37090096683 | | 1985 | 50.380760429379 | | 1984 | 50.402704598898 | | 1983 | 50.414749403139 | | 1982 | 50.395092497241 | | 1981 | 50.362779042267 | | 1980 | 50.326550480104 | | 1979 | 50.285114642005 | | 1978 | 50.237142990524 | | 1977 | 50.179154995044 | | 1976 | 50.11635754346 | | 1975 | 50.091505153167 | | 1974 | 50.107498223803 | | 1973 | 50.128082875001 | | 1972 | 50.153097244663 | | 1971 | 50.184811387021 | | 1970 | 50.219459349796 | | 1969 | 50.256776887517 | | 1968 | 50.299571390028 | | 1967 | 50.361113953683 | | 1966 | 50.455245712658 | | 1965 | 50.497500494696 | | 1964 | 50.461758361076 | | 1963 | 50.417154597148 | | 1962 | 50.367513798116 | | 1961 | 50.317487594379 | | 1960 | 50.262890877225 |
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