| Year | Value | | 2022 | 50.621260877103 | | 2021 | 50.636545881411 | | 2020 | 50.64769820319 | | 2019 | 50.665999387127 | | 2018 | 50.694518948082 | | 2017 | 50.724985844186 | | 2016 | 50.749059690123 | | 2015 | 50.771547967591 | | 2014 | 50.787479605163 | | 2013 | 50.797870181366 | | 2012 | 50.814162749808 | | 2011 | 50.83641942478 | | 2010 | 50.870120631229 | | 2009 | 50.918668987802 | | 2008 | 50.977671721499 | | 2007 | 51.045792604591 | | 2006 | 51.116656573533 | | 2005 | 51.180601086112 | | 2004 | 51.238216649588 | | 2003 | 51.297059494883 | | 2002 | 51.356392016177 | | 2001 | 51.417025648011 | | 2000 | 51.479543829275 | | 1999 | 51.543902130462 | | 1998 | 51.608655921155 | | 1997 | 51.672518794532 | | 1996 | 51.734802034422 | | 1995 | 51.793624654549 | | 1994 | 51.851558717271 | | 1993 | 51.918466047808 | | 1992 | 51.990047124823 | | 1991 | 51.992997166417 | | 1990 | 51.928028422467 | | 1989 | 51.862721071607 | | 1988 | 51.796757559036 | | 1987 | 51.732397216889 | | 1986 | 51.673375659204 | | 1985 | 51.623424524723 | | 1984 | 51.585287080251 | | 1983 | 51.560218229745 | | 1982 | 51.540895534643 | | 1981 | 51.605448808289 | | 1980 | 51.783762244587 | | 1979 | 52.004252937885 | | 1978 | 52.252193917075 | | 1977 | 52.522033091771 | | 1976 | 52.813977641619 | | 1975 | 53.126811643977 | | 1974 | 53.460753735347 | | 1973 | 53.816835705352 | | 1972 | 54.160462559109 | | 1971 | 54.361496278174 | | 1970 | 54.271550239428 | | 1969 | 53.965234849686 | | 1968 | 53.611485355828 | | 1967 | 53.253110728276 | | 1966 | 52.891598750989 | | 1965 | 52.529445247165 | | 1964 | 52.32911356385 | | 1963 | 52.288809032477 | | 1962 | 52.24373075231 | | 1961 | 52.190014168493 | | 1960 | 52.126583018923 |
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