| Year | Value | | 2021 | 60.050855891672 | | 2020 | 60.613995211007 | | 2019 | 61.086942542278 | | 2018 | 60.624156370152 | | 2017 | 60.35277941021 | | 2016 | 59.978337083583 | | 2015 | 59.527784202392 | | 2014 | 59.188017755797 | | 2013 | 58.82412632201 | | 2012 | 58.579870514343 | | 2011 | 58.439069444888 | | 2010 | 57.908371294273 | | 2009 | 57.398719357523 | | 2008 | 56.772210119393 | | 2007 | 56.222755591055 | | 2006 | 55.597593706641 | | 2005 | 54.739497992681 | | 2004 | 54.192737326891 | | 2003 | 53.702821700185 | | 2002 | 52.645557102368 | | 2001 | 52.162601065725 | | 2000 | 51.598504762432 | | 1999 | 50.28153586789 | | 1998 | 48.955303671404 | | 1997 | 49.624592781996 | | 1996 | 49.140506713455 | | 1995 | 49.016021878037 | | 1994 | 49.285681358 | | 1993 | 48.362406225553 | | 1992 | 47.562385735742 | | 1991 | 47.669870627174 | | 1990 | 47.52229662631 | | 1989 | 47.576232112714 | | 1988 | 45.866971219156 | | 1987 | 46.310667623625 | | 1986 | 45.666033054102 | | 1985 | 44.911850307902 | | 1984 | 44.459320380103 | | 1983 | 44.831100957168 | | 1982 | 46.017467163621 | | 1981 | 46.061056183363 | | 1980 | 45.872186202293 | | 1979 | 45.571321103821 | | 1978 | 45.138633265165 | | 1977 | 45.000131211976 | | 1976 | 44.675855844879 | | 1975 | 44.041637092312 | | 1974 | 43.743171134581 | | 1973 | 43.57507414085 | | 1972 | 42.78615725195 | | 1971 | 42.991587027941 | | 1970 | 42.536101265591 | | 1969 | 42.187364026115 | | 1968 | 41.899556164453 | | 1967 | 41.491787805669 | | 1966 | 40.772468553991 | | 1965 | 40.87923860514 | | 1964 | 40.844288144396 | | 1963 | 40.190020553131 | | 1962 | 40.154029431295 | | 1961 | 39.819326548837 | | 1960 | 39.524864524231 |
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