| Year | Value | | 2022 | 49.922734778938 | | 2021 | 49.927910222457 | | 2020 | 49.932005609802 | | 2019 | 49.940939418161 | | 2018 | 49.955958846679 | | 2017 | 49.972010706501 | | 2016 | 49.991125094491 | | 2015 | 50.015198747076 | | 2014 | 50.032776119864 | | 2013 | 50.042435835562 | | 2012 | 50.052719046018 | | 2011 | 50.063097806843 | | 2010 | 50.073773590173 | | 2009 | 50.086961130991 | | 2008 | 50.105338811887 | | 2007 | 50.123622842765 | | 2006 | 50.140448022913 | | 2005 | 50.156492312456 | | 2004 | 50.168771934395 | | 2003 | 50.179033228923 | | 2002 | 50.188081187802 | | 2001 | 50.196221900411 | | 2000 | 50.203126512525 | | 1999 | 50.210900223576 | | 1998 | 50.22240595583 | | 1997 | 50.233520146437 | | 1996 | 50.244031053311 | | 1995 | 50.253895776005 | | 1994 | 50.259399601186 | | 1993 | 50.260409559019 | | 1992 | 50.260401631032 | | 1991 | 50.259328068998 | | 1990 | 50.25643067438 | | 1989 | 50.254623174022 | | 1988 | 50.260163266086 | | 1987 | 50.26923567899 | | 1986 | 50.274448533162 | | 1985 | 50.279092091667 | | 1984 | 50.285846566089 | | 1983 | 50.294601835227 | | 1982 | 50.302153388788 | | 1981 | 50.309251453037 | | 1980 | 50.307154988234 | | 1979 | 50.309185580153 | | 1978 | 50.328958543893 | | 1977 | 50.34756926705 | | 1976 | 50.361201146149 | | 1975 | 50.378354601428 | | 1974 | 50.389075886162 | | 1973 | 50.390774242633 | | 1972 | 50.394929513722 | | 1971 | 50.431911655964 | | 1970 | 50.469522089022 | | 1969 | 50.475648197625 | | 1968 | 50.483860671922 | | 1967 | 50.493468314524 | | 1966 | 50.502637351567 | | 1965 | 50.510838261098 | | 1964 | 50.519659396282 | | 1963 | 50.528769286355 | | 1962 | 50.53760016538 | | 1961 | 50.548601078207 | | 1960 | 50.562883412401 |
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