| Year | Value | | 2022 | 48.693631773835 | | 2021 | 48.718900262639 | | 2020 | 48.742703259529 | | 2019 | 48.760303047608 | | 2018 | 48.76673713883 | | 2017 | 48.768100588516 | | 2016 | 48.76923368453 | | 2015 | 48.763498357956 | | 2014 | 48.759408097822 | | 2013 | 48.755256756885 | | 2012 | 48.734778082651 | | 2011 | 48.715866714784 | | 2010 | 48.704052332326 | | 2009 | 48.675184019823 | | 2008 | 48.638406501696 | | 2007 | 48.595952354955 | | 2006 | 48.547059892972 | | 2005 | 48.499782737507 | | 2004 | 48.453469713617 | | 2003 | 48.441451029571 | | 2002 | 48.473694441766 | | 2001 | 48.515555274735 | | 2000 | 48.554610278467 | | 1999 | 48.595522018295 | | 1998 | 48.652869603078 | | 1997 | 48.715370884476 | | 1996 | 48.765410645114 | | 1995 | 48.814047900061 | | 1994 | 48.853983086305 | | 1993 | 48.89906187555 | | 1992 | 48.96306150574 | | 1991 | 49.024728219997 | | 1990 | 49.073928057647 | | 1989 | 49.101576408895 | | 1988 | 49.114961409289 | | 1987 | 49.114701601641 | | 1986 | 49.100849366966 | | 1985 | 49.079424830721 | | 1984 | 49.056613179002 | | 1983 | 49.029583034388 | | 1982 | 48.990063118961 | | 1981 | 48.942197952402 | | 1980 | 48.897211041804 | | 1979 | 48.851178649734 | | 1978 | 48.797299661072 | | 1977 | 48.736975110517 | | 1976 | 48.669200848344 | | 1975 | 48.593099329673 | | 1974 | 48.510740598813 | | 1973 | 48.424293924691 | | 1972 | 48.334180115101 | | 1971 | 48.253175619904 | | 1970 | 48.206001493584 | | 1969 | 48.183474501248 | | 1968 | 48.156417919633 | | 1967 | 48.122751470837 | | 1966 | 48.082610361666 | | 1965 | 48.034531825083 | | 1964 | 47.978537985715 | | 1963 | 47.915746988712 | | 1962 | 47.843029027355 | | 1961 | 47.768869528572 | | 1960 | 47.723054417541 |
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