| Year | Value | | 2022 | 49.904913061862 | | 2021 | 49.929681887955 | | 2020 | 49.955151897042 | | 2019 | 49.983297853502 | | 2018 | 50.014976336944 | | 2017 | 50.039842344856 | | 2016 | 50.052156519017 | | 2015 | 50.075850526618 | | 2014 | 50.113164556025 | | 2013 | 50.147182499197 | | 2012 | 50.181076336489 | | 2011 | 50.215307828347 | | 2010 | 50.245459161439 | | 2009 | 50.271240026095 | | 2008 | 50.283966794738 | | 2007 | 50.26855240035 | | 2006 | 50.236492179528 | | 2005 | 50.213922701125 | | 2004 | 50.203575526255 | | 2003 | 50.201285072498 | | 2002 | 50.217172938857 | | 2001 | 50.24719709374 | | 2000 | 50.278620307933 | | 1999 | 50.312093657567 | | 1998 | 50.35229376136 | | 1997 | 50.397554584996 | | 1996 | 50.44454237312 | | 1995 | 50.491601976585 | | 1994 | 50.537974650723 | | 1993 | 50.584888393952 | | 1992 | 50.63588371228 | | 1991 | 50.675291087077 | | 1990 | 50.686073655337 | | 1989 | 50.682175066891 | | 1988 | 50.646057365288 | | 1987 | 50.592127891889 | | 1986 | 50.550497172413 | | 1985 | 50.50395281003 | | 1984 | 50.453605091022 | | 1983 | 50.398943566972 | | 1982 | 50.341388482274 | | 1981 | 50.278725210169 | | 1980 | 50.232678835531 | | 1979 | 50.235185127813 | | 1978 | 50.265633996159 | | 1977 | 50.296656744776 | | 1976 | 50.327842976723 | | 1975 | 50.346249860772 | | 1974 | 50.350916015855 | | 1973 | 50.367108073214 | | 1972 | 50.396204929613 | | 1971 | 50.42562586362 | | 1970 | 50.454081381486 | | 1969 | 50.478840976594 | | 1968 | 50.501216015671 | | 1967 | 50.52379487511 | | 1966 | 50.541596138268 | | 1965 | 50.554727718032 | | 1964 | 50.566484800857 | | 1963 | 50.574004786045 | | 1962 | 50.579523838546 | | 1961 | 50.579529781782 | | 1960 | 50.570315263446 |
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