| Year | Value | | 2021 | 62.417067685561 | | 2020 | 62.832792543096 | | 2019 | 63.334253939145 | | 2018 | 63.033853282508 | | 2017 | 62.63612064157 | | 2016 | 62.251717627298 | | 2015 | 61.782542107593 | | 2014 | 61.427968483193 | | 2013 | 61.008363923565 | | 2012 | 60.830189374751 | | 2011 | 60.605974913877 | | 2010 | 60.04716206381 | | 2009 | 59.561787051032 | | 2008 | 58.8231088431 | | 2007 | 58.67112449239 | | 2006 | 58.316621870595 | | 2005 | 57.781589592561 | | 2004 | 57.259661132988 | | 2003 | 56.900212814779 | | 2002 | 56.455868076419 | | 2001 | 56.099333045955 | | 2000 | 55.672685271866 | | 1999 | 55.111102907962 | | 1998 | 53.833662360668 | | 1997 | 53.731184915435 | | 1996 | 53.212299382732 | | 1995 | 53.019655979368 | | 1994 | 52.664053076965 | | 1993 | 52.000633358143 | | 1992 | 51.514979062947 | | 1991 | 51.035802784681 | | 1990 | 51.296027609278 | | 1989 | 50.975307665971 | | 1988 | 49.978718422066 | | 1987 | 50.08135992651 | | 1986 | 49.569931716781 | | 1985 | 48.959425555827 | | 1984 | 48.626186569694 | | 1983 | 48.664387799026 | | 1982 | 49.101050222752 | | 1981 | 48.963456416114 | | 1980 | 48.687730024612 | | 1979 | 48.181956546699 | | 1978 | 47.768595055649 | | 1977 | 47.503380148593 | | 1976 | 46.934597469295 | | 1975 | 46.31259579797 | | 1974 | 46.166893643655 | | 1973 | 46.100466855904 | | 1972 | 45.546441617779 | | 1971 | 40.080429217796 | | 1970 | 44.036729917139 | | 1969 | 45.042456476503 | | 1968 | 44.795901886499 | | 1967 | 44.42493341336 | | 1966 | 43.906604970246 | | 1965 | 43.503795895463 | | 1964 | 43.47044213395 | | 1963 | 42.815268858488 | | 1962 | 42.668747234495 | | 1961 | 42.140450895492 | | 1960 | 41.691355977822 |
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