| Year | Value | | 2021 | 64.67721008304 | | 2020 | 65.043479795382 | | 2019 | 65.550231008565 | | 2018 | 65.12106924161 | | 2017 | 64.644494671671 | | 2016 | 64.249008979858 | | 2015 | 63.638667277265 | | 2014 | 63.116750208287 | | 2013 | 62.586730425939 | | 2012 | 61.90270136462 | | 2011 | 61.226773769105 | | 2010 | 60.225017505029 | | 2009 | 59.872416046516 | | 2008 | 59.059354855408 | | 2007 | 58.402928940082 | | 2006 | 57.678251760873 | | 2005 | 56.855301881971 | | 2004 | 56.133524854907 | | 2003 | 55.618005913793 | | 2002 | 55.024094120843 | | 2001 | 54.533550881164 | | 2000 | 54.097068164576 | | 1999 | 53.606031945383 | | 1998 | 52.818498557302 | | 1997 | 52.805639365232 | | 1996 | 52.477277092126 | | 1995 | 52.356355506337 | | 1994 | 51.772475407869 | | 1993 | 51.589107128028 | | 1992 | 51.038880727659 | | 1991 | 51.037961276909 | | 1990 | 51.202315329104 | | 1989 | 51.104590388568 | | 1988 | 50.273538354541 | | 1987 | 50.471939018968 | | 1986 | 49.581328129587 | | 1985 | 48.796957947752 | | 1984 | 48.486812898893 | | 1983 | 48.41468113564 | | 1982 | 49.610873531575 | | 1981 | 49.326290467363 | | 1980 | 49.003852837974 | | 1979 | 48.611915443991 | | 1978 | 48.160331518027 | | 1977 | 47.876428755746 | | 1976 | 47.485098063884 | | 1975 | 46.732000463178 | | 1974 | 46.35927922722 | | 1973 | 46.339391340107 | | 1972 | 45.661275007054 | | 1971 | 45.883432926474 | | 1970 | 45.494036810268 | | 1969 | 45.18268353435 | | 1968 | 44.898335715712 | | 1967 | 44.571408963927 | | 1966 | 43.893042752599 | | 1965 | 44.016852038055 | | 1964 | 43.853790108523 | | 1963 | 43.322239051362 | | 1962 | 43.098002107123 | | 1961 | 42.744320717716 | | 1960 | 42.383892629137 |
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