| Year | Value | | 2024 | 50.342845165734 | | 2023 | 50.340916169488 | | 2022 | 50.330422041943 | | 2021 | 50.316354144801 | | 2020 | 50.318303508122 | | 2019 | 50.331481659643 | | 2018 | 50.355472535799 | | 2017 | 50.382135950838 | | 2016 | 50.396158878809 | | 2015 | 50.398907364876 | | 2014 | 50.399291266386 | | 2013 | 50.408377671846 | | 2012 | 50.42760092085 | | 2011 | 50.446289909729 | | 2010 | 50.454536828032 | | 2009 | 50.45510351835 | | 2008 | 50.454384626665 | | 2007 | 50.451093099936 | | 2006 | 50.448001263524 | | 2005 | 50.451898021629 | | 2004 | 50.459063837103 | | 2003 | 50.463201304717 | | 2002 | 50.468147436524 | | 2001 | 50.482261308349 | | 2000 | 50.504501145498 | | 1999 | 50.520638357775 | | 1998 | 50.521452890374 | | 1997 | 50.521561049305 | | 1996 | 50.529080577098 | | 1995 | 50.525548410591 | | 1994 | 50.510898389121 | | 1993 | 50.495103524768 | | 1992 | 50.467300770595 | | 1991 | 50.443794789233 | | 1990 | 50.441714518773 | | 1989 | 50.430690581944 | | 1988 | 50.405322441253 | | 1987 | 50.387722053343 | | 1986 | 50.380154828705 | | 1985 | 50.36596711765 | | 1984 | 50.337328535325 | | 1983 | 50.302007570415 | | 1982 | 50.266481952942 | | 1981 | 50.232733197174 | | 1980 | 50.199761341263 | | 1979 | 50.163698966199 | | 1978 | 50.11654699607 | | 1977 | 50.06047110998 | | 1976 | 50.004220708073 |
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