| Year | Value | | 2022 | 59.557470652026 | | 2021 | 59.294886466977 | | 2020 | 59.087619011041 | | 2019 | 58.883816974964 | | 2018 | 58.629576156389 | | 2017 | 58.371289966706 | | 2016 | 58.123255382143 | | 2015 | 57.846153132278 | | 2014 | 57.507260831792 | | 2013 | 57.177973821031 | | 2012 | 56.864221351156 | | 2011 | 56.637995129467 | | 2010 | 56.380417555645 | | 2009 | 55.996756942822 | | 2008 | 55.559292394188 | | 2007 | 55.119668255135 | | 2006 | 54.834300381715 | | 2005 | 54.435223067207 | | 2004 | 54.095522468637 | | 2003 | 53.830162111699 | | 2002 | 53.566432758694 | | 2001 | 53.31180114924 | | 2000 | 53.055997379554 | | 1999 | 52.810525933373 | | 1998 | 52.562001040093 | | 1997 | 52.316174722288 | | 1996 | 52.091923887961 | | 1995 | 51.898503584799 | | 1994 | 51.702414169609 | | 1993 | 51.434808929541 | | 1992 | 51.019026706105 | | 1991 | 50.471175220027 | | 1990 | 50.074412080139 | | 1989 | 49.595084671918 | | 1988 | 49.099801922866 | | 1987 | 48.575167738673 | | 1986 | 48.005319311411 | | 1985 | 47.389662394081 | | 1984 | 46.776466984488 | | 1983 | 46.138776943154 | | 1982 | 45.571166218622 | | 1981 | 45.034321833112 | | 1980 | 44.483792258035 | | 1979 | 43.971767191378 | | 1978 | 43.54181166897 | | 1977 | 43.06607490166 | | 1976 | 42.444465738345 | | 1975 | 41.798750885946 | | 1974 | 41.197729901881 | | 1973 | 40.566237699963 | | 1972 | 39.871091492965 | | 1971 | 39.169000703256 | | 1970 | 38.481548394717 | | 1969 | 37.767112875064 | | 1968 | 37.057048855005 | | 1967 | 36.357628131913 | | 1966 | 35.673253908897 | | 1965 | 34.882985099842 | | 1964 | 34.053793204814 | | 1963 | 33.261492667825 | | 1962 | 32.494831780935 | | 1961 | 31.754677450086 | | 1960 | 31.022161876125 |
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