| Year | Value | | 2023 | 50.150858850761 | | 2022 | 50.167148290413 | | 2021 | 50.195222092995 | | 2020 | 50.227219727003 | | 2019 | 50.249437533787 | | 2018 | 50.268414107019 | | 2017 | 50.287970913731 | | 2016 | 50.307347028584 | | 2015 | 50.325282756271 | | 2014 | 50.342613576829 | | 2013 | 50.359384893532 | | 2012 | 50.374918941945 | | 2011 | 50.389474815659 | | 2010 | 50.404071404334 | | 2009 | 50.419670347051 | | 2008 | 50.435720707649 | | 2007 | 50.451101893068 | | 2006 | 50.465300926569 | | 2005 | 50.47827700603 | | 2004 | 50.490351647887 | | 2003 | 50.501338887515 | | 2002 | 50.505879884318 | | 2001 | 50.504367068965 | | 2000 | 50.502894801434 | | 1999 | 50.5012357252 | | 1998 | 50.499048474242 | | 1997 | 50.49616094737 | | 1996 | 50.492496710431 | | 1995 | 50.487880927707 | | 1994 | 50.482128935385 | | 1993 | 50.475531643736 | | 1992 | 50.467944909711 | | 1991 | 50.459201942686 | | 1990 | 50.449123792943 | | 1989 | 50.437789267944 | | 1988 | 50.424101685989 | | 1987 | 50.408087673168 | | 1986 | 50.391336058352 | | 1985 | 50.373760457759 | | 1984 | 50.355207363982 | | 1983 | 50.335918371775 | | 1982 | 50.315976626285 | | 1981 | 50.284723539133 | | 1980 | 50.240318874898 | | 1979 | 50.189326243364 | | 1978 | 50.130187988765 | | 1977 | 50.065703068807 | | 1976 | 49.998368877309 | | 1975 | 49.929819946739 |
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