| Year | Value | | 2022 | 52.864859786744 | | 2021 | 52.87364953021 | | 2020 | 52.890181545246 | | 2019 | 52.84943913117 | | 2018 | 52.787791849909 | | 2017 | 52.723375601058 | | 2016 | 52.657474683906 | | 2015 | 52.589274581083 | | 2014 | 52.515589705967 | | 2013 | 52.442651632971 | | 2012 | 52.373863992479 | | 2011 | 52.306294921412 | | 2010 | 52.305637775187 | | 2009 | 52.331371205096 | | 2008 | 52.320502877669 | | 2007 | 52.316943391158 | | 2006 | 52.314708281907 | | 2005 | 52.299355439603 | | 2004 | 52.252512294206 | | 2003 | 52.182824349252 | | 2002 | 52.114272017084 | | 2001 | 52.020597413194 | | 2000 | 51.928710115487 | | 1999 | 51.860890787065 | | 1998 | 51.790646671804 | | 1997 | 51.718830169318 | | 1996 | 51.643854590327 | | 1995 | 51.55613238157 | | 1994 | 51.448266630973 | | 1993 | 51.322553897181 | | 1992 | 51.203840893549 | | 1991 | 51.068313096782 | | 1990 | 50.949598246895 | | 1989 | 50.919561582761 | | 1988 | 50.966859416775 | | 1987 | 51.053529868115 | | 1986 | 51.131628274441 | | 1985 | 51.192654859022 | | 1984 | 51.245052513479 | | 1983 | 51.283702086899 | | 1982 | 51.316623360162 | | 1981 | 51.300028747564 | | 1980 | 51.245443011547 | | 1979 | 51.203109376512 | | 1978 | 51.15811979656 | | 1977 | 51.112014967868 | | 1976 | 51.059761737454 | | 1975 | 51.012105739933 | | 1974 | 50.967881655228 | | 1973 | 50.920576097027 | | 1972 | 50.892872313312 | | 1971 | 50.882412948857 | | 1970 | 50.862856562786 | | 1969 | 50.844429462329 | | 1968 | 50.834860688403 | | 1967 | 50.826585128188 | | 1966 | 50.825589043868 | | 1965 | 50.823381307203 | | 1964 | 50.826773006979 | | 1963 | 50.836015658982 | | 1962 | 50.845065452877 | | 1961 | 50.850190822598 | | 1960 | 50.858848520363 |
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