| Year | Value | | 2022 | 50.399999717052 | | 2021 | 50.385313833352 | | 2020 | 50.37402018695 | | 2019 | 50.363551004292 | | 2018 | 50.352207722004 | | 2017 | 50.343614957541 | | 2016 | 50.339655224703 | | 2015 | 50.34330609477 | | 2014 | 50.357527249534 | | 2013 | 50.378435334238 | | 2012 | 50.398921377758 | | 2011 | 50.412119574578 | | 2010 | 50.418450445811 | | 2009 | 50.425121060417 | | 2008 | 50.434226497055 | | 2007 | 50.441818718276 | | 2006 | 50.444331253764 | | 2005 | 50.443111956047 | | 2004 | 50.441512538926 | | 2003 | 50.443771413871 | | 2002 | 50.451967293397 | | 2001 | 50.46623282884 | | 2000 | 50.486160159712 | | 1999 | 50.510597699547 | | 1998 | 50.540622463922 | | 1997 | 50.576527013794 | | 1996 | 50.615896283066 | | 1995 | 50.660922334353 | | 1994 | 50.712709455265 | | 1993 | 50.768382415734 | | 1992 | 50.827290523927 | | 1991 | 50.870715507945 | | 1990 | 50.896393439882 | | 1989 | 50.920570582275 | | 1988 | 50.945534768272 | | 1987 | 50.973207005258 | | 1986 | 51.002495389424 | | 1985 | 51.035806686649 | | 1984 | 51.07555115841 | | 1983 | 51.123978964359 | | 1982 | 51.176847126258 | | 1981 | 51.228920867493 | | 1980 | 51.279063995812 | | 1979 | 51.326119385629 | | 1978 | 51.368743345903 | | 1977 | 51.406254334096 | | 1976 | 51.439083590623 | | 1975 | 51.466880735502 | | 1974 | 51.493812282265 | | 1973 | 51.520366829108 | | 1972 | 51.544432488087 | | 1971 | 51.562527337535 | | 1970 | 51.607909456826 | | 1969 | 51.687956328712 | | 1968 | 51.771843093153 | | 1967 | 51.859397513655 | | 1966 | 51.950725999447 | | 1965 | 52.044875233045 | | 1964 | 52.141601374001 | | 1963 | 52.236030021105 | | 1962 | 52.32630996917 | | 1961 | 52.416402905718 | | 1960 | 52.507442166043 |
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