| Year | Value | | 2021 | 47.485617791007 | | 2020 | 47.497066315579 | | 2019 | 47.700277626721 | | 2018 | 47.641536435972 | | 2017 | 47.763116466783 | | 2016 | 47.684337073506 | | 2015 | 47.959066674311 | | 2014 | 47.936371453138 | | 2013 | 47.858862646182 | | 2012 | 47.810868193034 | | 2011 | 47.965916915309 | | 2010 | 47.910032418166 | | 2009 | 48.43808267118 | | 2008 | 48.535696870608 | | 2007 | 48.61330197608 | | 2006 | 48.594861206699 | | 2005 | 48.83300837252 | | 2004 | 48.779998279669 | | 2003 | 48.740001720134 | | 2002 | 48.635555810354 | | 2001 | 48.822012037833 | | 2000 | 48.912451640636 | | 1999 | 49.148948363803 | | 1998 | 49.776517105037 | | 1997 | 49.640452657212 | | 1996 | 49.663410581798 | | 1995 | 49.679175021484 | | 1994 | 49.577497063963 | | 1993 | 49.157882676444 | | 1992 | 48.552115257927 | | 1991 | 49.082003838112 | | 1990 | 51.648383123765 | | 1989 | 51.717125426059 | | 1988 | 51.834560192478 | | 1987 | 51.914759545155 | | 1986 | 52.15249334059 | | 1985 | 52.255606794031 | | 1984 | 52.370177297855 | | 1983 | 52.501933377252 | | 1982 | 52.690974708561 | | 1981 | 52.877151777275 | | 1980 | 53.043279007819 | | 1979 | 53.258098702489 | | 1978 | 53.444275771203 | | 1977 | 53.587488900982 | | 1976 | 53.727837768167 | | 1975 | 53.825222696417 | | 1974 | 53.908286311689 | | 1973 | 54.125970268954 | | 1972 | 54.274911923925 | | 1971 | 54.283504711712 | | 1970 | 54.486867355999 | | 1969 | 55.148512015582 | | 1968 | 55.237304156045 | | 1967 | 55.601065505686 | | 1966 | 55.941912754561 | | 1965 | 55.950505542348 | | 1964 | 55.732821585083 | | 1963 | 55.57242287973 | | 1962 | 55.546644516369 | | 1961 | 55.495087789649 |
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