| Year | Value | | 2021 | 47.259237495482 | | 2020 | 46.252479842746 | | 2019 | 47.123772429089 | | 2018 | 46.658095012753 | | 2017 | 48.340617939111 | | 2016 | 44.539925793225 | | 2015 | 45.31442406571 | | 2014 | 48.738398656652 | | 2013 | 48.393710216992 | | 2012 | 50.385431446312 | | 2011 | 51.562813219999 | | 2010 | 48.992098720435 | | 2009 | 50.018484047746 | | 2008 | 50.67336604923 | | 2007 | 51.8536766333 | | 2006 | 53.27857542663 | | 2005 | 53.399372583731 | | 2004 | 51.404657459355 | | 2003 | 57.209429467738 | | 2002 | 58.185699595173 | | 2001 | 59.318172942999 | | 2000 | 59.288103823074 | | 1999 | 59.056923056897 | | 1998 | 60.383088398006 | | 1997 | 60.168569308671 | | 1996 | 60.558686851594 | | 1995 | 60.318914908296 | | 1994 | 61.068039519415 | | 1993 | 59.890527576377 | | 1992 | 60.659437928745 | | 1991 | 60.240032281999 | | 1990 | 60.455462556786 | | 1989 | 60.802624214103 | | 1988 | 61.446702159509 | | 1987 | 61.312367389974 | | 1986 | 60.989677570519 | | 1985 | 63.365268213946 | | 1984 | 63.334938755321 | | 1983 | 62.974499824271 | | 1982 | 63.883472397589 | | 1981 | 64.507374093696 | | 1980 | 64.51687645627 | | 1979 | 64.20447001549 | | 1978 | 64.57701469612 | | 1977 | 63.979537378129 | | 1976 | 65.181260820327 | | 1975 | 65.025708446689 | | 1974 | 65.131145620452 | | 1973 | 64.810929018653 | | 1972 | 65.060593832576 | | 1971 | 65.024298283066 | | 1970 | 64.229787758874 | | 1969 | 66.501961508923 | | 1968 | 66.851016114966 | | 1967 | 63.728383934499 | | 1966 | 63.396186780001 | | 1965 | 63.296042981919 | | 1964 | 62.729105814665 | | 1963 | 62.399226559754 | | 1962 | 62.037792262734 | | 1961 | 61.763331879776 |
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