| Year | Value | | 2021 | 47.470851153047 | | 2020 | 47.16158173785 | | 2019 | 47.452849768503 | | 2018 | 47.325934810457 | | 2017 | 47.870884154321 | | 2016 | 46.548733092697 | | 2015 | 46.752263888472 | | 2014 | 47.776032130093 | | 2013 | 47.693655513646 | | 2012 | 48.316584621764 | | 2011 | 48.702569171609 | | 2010 | 47.871111552424 | | 2009 | 48.193713178479 | | 2008 | 48.329345077585 | | 2007 | 48.637829374076 | | 2006 | 48.985685548225 | | 2005 | 48.915414915088 | | 2004 | 48.252656254147 | | 2003 | 49.989766134717 | | 2002 | 50.873062167774 | | 2001 | 51.150978216129 | | 2000 | 51.037426994228 | | 1999 | 50.985884575334 | | 1998 | 51.262121164542 | | 1997 | 51.166660616448 | | 1996 | 50.826910922245 | | 1995 | 50.72922215243 | | 1994 | 50.932287765874 | | 1993 | 50.397153019921 | | 1992 | 50.640826424243 | | 1991 | 50.505396679817 | | 1990 | 50.466612096503 | | 1989 | 50.290084421273 | | 1988 | 50.195528029167 | | 1987 | 49.850495173259 | | 1986 | 49.380839481541 | | 1985 | 49.780135395409 | | 1984 | 49.143519733842 | | 1983 | 48.597177559938 | | 1982 | 48.430148864489 | | 1981 | 48.230250251833 | | 1980 | 47.971004235495 | | 1979 | 47.656699615839 | | 1978 | 47.611560138227 | | 1977 | 47.14249040427 | | 1976 | 47.221793343576 | | 1975 | 47.495167401516 | | 1974 | 47.288336244556 | | 1973 | 46.86530287574 | | 1972 | 46.687564277178 | | 1971 | 46.426065736819 | | 1970 | 46.025348954932 | | 1969 | 46.527147848087 | | 1968 | 46.456107978675 | | 1967 | 45.312417621279 | | 1966 | 45.038169675191 | | 1965 | 44.84633084906 | | 1964 | 44.497677114283 | | 1963 | 44.241924184546 | | 1962 | 43.986368609892 | | 1961 | 43.762206118464 |
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