| Year | Value | | 2021 | 44.975027499514 | | 2020 | 45.020421382013 | | 2019 | 44.862428655327 | | 2018 | 44.961176237417 | | 2017 | 44.937469181614 | | 2016 | 44.838614401761 | | 2015 | 44.665073199881 | | 2014 | 44.684728086637 | | 2013 | 44.539788604807 | | 2012 | 44.488121522363 | | 2011 | 44.508396428222 | | 2010 | 44.219210559602 | | 2009 | 44.159108110546 | | 2008 | 44.144502535082 | | 2007 | 44.231590103458 | | 2006 | 44.274810380335 | | 2005 | 44.184405793938 | | 2004 | 44.182630211312 | | 2003 | 44.250997808828 | | 2002 | 44.214785744179 | | 2001 | 44.217753861349 | | 2000 | 44.039009711331 | | 1999 | 44.1226858792 | | 1998 | 43.917681496417 | | 1997 | 43.780970712025 | | 1996 | 43.552461796552 | | 1995 | 43.568198619023 | | 1994 | 42.987945630606 | | 1993 | 42.626419827115 | | 1992 | 42.483415229198 | | 1991 | 39.61744638017 | | 1990 | 39.345502120959 | | 1989 | 39.411795728669 | | 1988 | 39.124359465209 | | 1987 | 39.319431942941 | | 1986 | 38.990458852375 | | 1985 | 39.279913386765 | | 1984 | 39.040484587864 | | 1983 | 38.670223150785 | | 1982 | 39.140003600433 | | 1981 | 38.562362289774 | | 1980 | 38.733940673991 | | 1979 | 38.38447047011 | | 1978 | 38.246994779372 | | 1977 | 38.072804813424 | | 1976 | 38.005106529715 | | 1975 | 37.999274842354 | | 1974 | 37.762178718398 | | 1973 | 37.829648805645 | | 1972 | 37.530711440503 | | 1971 | 37.44830716258 | | 1970 | 37.465295121413 | | 1969 | 37.340801273843 | | 1968 | 37.60931244406 | | 1967 | 37.608044685938 | | 1966 | 37.612101511928 | | 1965 | 37.511695068674 | | 1964 | 37.21960359739 | | 1963 | 37.016255194639 | | 1962 | 36.930808297223 | | 1961 | 36.824823718233 |
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