| Year | Value | | 2022 | 51.293656791779 | | 2021 | 51.310781538052 | | 2020 | 51.337130867499 | | 2019 | 51.389332821923 | | 2018 | 51.444771462942 | | 2017 | 51.504281369418 | | 2016 | 51.56234351883 | | 2015 | 51.617966938633 | | 2014 | 51.675524489889 | | 2013 | 51.728812347784 | | 2012 | 51.777024398634 | | 2011 | 51.822860296858 | | 2010 | 51.867886012303 | | 2009 | 51.909003155999 | | 2008 | 51.941432025753 | | 2007 | 51.968661219576 | | 2006 | 51.994223055261 | | 2005 | 52.01498708372 | | 2004 | 52.030359976144 | | 2003 | 52.041059469342 | | 2002 | 52.04554316567 | | 2001 | 52.043763600405 | | 2000 | 52.001458084255 | | 1999 | 51.922653082983 | | 1998 | 51.850735160942 | | 1997 | 51.788979560735 | | 1996 | 51.735290087815 | | 1995 | 51.701379209919 | | 1994 | 51.699455495323 | | 1993 | 51.714181799819 | | 1992 | 51.711004745201 | | 1991 | 51.669163645041 | | 1990 | 51.634679721206 | | 1989 | 51.630612069882 | | 1988 | 51.630267243314 | | 1987 | 51.63335300359 | | 1986 | 51.640550510242 | | 1985 | 51.64807711325 | | 1984 | 51.654732199946 | | 1983 | 51.661086430873 | | 1982 | 51.672490999159 | | 1981 | 51.682979094299 | | 1980 | 51.683666143606 | | 1979 | 51.677170475169 | | 1978 | 51.667499681283 | | 1977 | 51.660528596891 | | 1976 | 51.659241480286 | | 1975 | 51.664487355189 | | 1974 | 51.67419612303 | | 1973 | 51.687659670173 | | 1972 | 51.707329358748 | | 1971 | 51.738184076154 | | 1970 | 51.780468401861 | | 1969 | 51.831139574126 | | 1968 | 51.891352339317 | | 1967 | 51.959038340549 | | 1966 | 52.036008201237 | | 1965 | 52.119913592524 | | 1964 | 52.203767619901 | | 1963 | 52.286430983507 | | 1962 | 52.363312494904 | | 1961 | 52.431111065075 | | 1960 | 52.486997440766 |
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