| Year | Value | | 2022 | 50.583619033782 | | 2021 | 50.597396392764 | | 2020 | 50.607459283084 | | 2019 | 50.624853068703 | | 2018 | 50.649851046151 | | 2017 | 50.678082689839 | | 2016 | 50.708531051225 | | 2015 | 50.742208846988 | | 2014 | 50.77669721249 | | 2013 | 50.811166201419 | | 2012 | 50.848759292753 | | 2011 | 50.885252339201 | | 2010 | 50.919794680179 | | 2009 | 50.954485471531 | | 2008 | 50.991547087499 | | 2007 | 51.030723199986 | | 2006 | 51.067425173139 | | 2005 | 51.103928787718 | | 2004 | 51.140941396098 | | 2003 | 51.178298186721 | | 2002 | 51.214552471717 | | 2001 | 51.246527111209 | | 2000 | 51.275247156574 | | 1999 | 51.303053411498 | | 1998 | 51.328476737037 | | 1997 | 51.350443478321 | | 1996 | 51.369098414345 | | 1995 | 51.382879278991 | | 1994 | 51.392820740008 | | 1993 | 51.401162267973 | | 1992 | 51.406808714565 | | 1991 | 51.409537475723 | | 1990 | 51.409705941443 | | 1989 | 51.409159900714 | | 1988 | 51.407453433947 | | 1987 | 51.402066809814 | | 1986 | 51.394804078262 | | 1985 | 51.387062612895 | | 1984 | 51.378130768861 | | 1983 | 51.368267156696 | | 1982 | 51.360599982997 | | 1981 | 51.355172506855 | | 1980 | 51.35123667213 | | 1979 | 51.350949825891 | | 1978 | 51.354023117181 | | 1977 | 51.359418926252 | | 1976 | 51.368874436506 | | 1975 | 51.380487996821 | | 1974 | 51.394126547717 | | 1973 | 51.411617538741 | | 1972 | 51.430738343426 | | 1971 | 51.450851720463 | | 1970 | 51.471122296383 | | 1969 | 51.488299847932 | | 1968 | 51.505926019215 | | 1967 | 51.525566607774 | | 1966 | 51.544925301457 | | 1965 | 51.564676943287 | | 1964 | 51.586597105539 | | 1963 | 51.61098288022 | | 1962 | 51.637430540187 | | 1961 | 51.667418919011 | | 1960 | 51.699364731949 |
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