| Year | Value | | 2021 | 61.734065726693 | | 2020 | 62.04854117807 | | 2019 | 62.431653805765 | | 2018 | 62.035157044396 | | 2017 | 61.651929637451 | | 2016 | 61.162845242452 | | 2015 | 60.727929968662 | | 2014 | 60.365895716252 | | 2013 | 59.897372980772 | | 2012 | 59.364851584494 | | 2011 | 58.855554967275 | | 2010 | 58.243316133659 | | 2009 | 57.710753857232 | | 2008 | 57.037616778518 | | 2007 | 56.5960868624 | | 2006 | 56.088318113094 | | 2005 | 55.43151727952 | | 2004 | 54.830635938226 | | 2003 | 54.373973294442 | | 2002 | 53.837878319023 | | 2001 | 53.432033660387 | | 2000 | 53.016855351337 | | 1999 | 52.517980468196 | | 1998 | 51.517281987356 | | 1997 | 51.744148347079 | | 1996 | 51.561164748814 | | 1995 | 51.534339845039 | | 1994 | 51.693753521339 | | 1993 | 51.03400146584 | | 1992 | 50.529987888582 | | 1991 | 50.592703137187 | | 1990 | 50.800891069165 | | 1989 | 50.705591715944 | | 1988 | 49.859315913375 | | 1987 | 50.262976247776 | | 1986 | 50.538499361729 | | 1985 | 50.061478120902 | | 1984 | 49.924686376761 | | 1983 | 49.994856973803 | | 1982 | 50.16721379551 | | 1981 | 49.956523890426 | | 1980 | 49.571933718705 | | 1979 | 49.225105072569 | | 1978 | 48.869831260066 | | 1977 | 48.497983006306 | | 1976 | 47.885194939389 | | 1975 | 47.295649633288 | | 1974 | 46.863859856647 | | 1973 | 46.376779354257 | | 1972 | 45.621927628421 | | 1971 | 45.311828240769 | | 1970 | 44.706007380422 | | 1969 | 44.287990997252 | | 1968 | 43.984972582134 | | 1967 | 43.473824568511 | | 1966 | 43.271591678793 | | 1965 | 43.07888832816 | | 1964 | 42.898397305562 | | 1963 | 42.440053253784 | | 1962 | 42.06327671654 | | 1961 | 41.731242887062 | | 1960 | 41.371588107675 |
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