| Year | Value | | 2022 | 48.869858336287 | | 2021 | 48.854907838986 | | 2020 | 48.852674493554 | | 2019 | 48.846431667212 | | 2018 | 48.834599355698 | | 2017 | 48.818745612747 | | 2016 | 48.801576991927 | | 2015 | 48.781580942057 | | 2014 | 48.763848426873 | | 2013 | 48.753048056772 | | 2012 | 48.742924117962 | | 2011 | 48.732767702105 | | 2010 | 48.725582657351 | | 2009 | 48.718499154613 | | 2008 | 48.708946342657 | | 2007 | 48.695322504026 | | 2006 | 48.68159671528 | | 2005 | 48.666957265093 | | 2004 | 48.649580784891 | | 2003 | 48.634072621366 | | 2002 | 48.621903231843 | | 2001 | 48.616822940509 | | 2000 | 48.613424633337 | | 1999 | 48.612063787577 | | 1998 | 48.616907750597 | | 1997 | 48.620289231903 | | 1996 | 48.621534787282 | | 1995 | 48.621283239596 | | 1994 | 48.618568155216 | | 1993 | 48.611887343084 | | 1992 | 48.602878548809 | | 1991 | 48.59277783417 | | 1990 | 48.581638155337 | | 1989 | 48.570938102977 | | 1988 | 48.561846692096 | | 1987 | 48.552951060494 | | 1986 | 48.543101523838 | | 1985 | 48.534735408113 | | 1984 | 48.528518082117 | | 1983 | 48.522623361227 | | 1982 | 48.51652498 | | 1981 | 48.511212667096 | | 1980 | 48.497747271187 | | 1979 | 48.485092385766 | | 1978 | 48.481788581263 | | 1977 | 48.47677833013 | | 1976 | 48.470989166827 | | 1975 | 48.465094441314 | | 1974 | 48.454778313931 | | 1973 | 48.442608626858 | | 1972 | 48.430988526595 | | 1971 | 48.416484380075 | | 1970 | 48.400966983697 | | 1969 | 48.387376154806 | | 1968 | 48.372336495016 | | 1967 | 48.352373663292 | | 1966 | 48.328875173076 | | 1965 | 48.302397047146 | | 1964 | 48.273150963344 | | 1963 | 48.242589059074 | | 1962 | 48.211094088589 | | 1961 | 48.179913183206 | | 1960 | 48.149454367172 |
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