| Year | Value | | 2021 | 62.496109508007 | | 2020 | 62.954532536461 | | 2019 | 63.4239909431 | | 2018 | 62.995203917953 | | 2017 | 62.623713909071 | | 2016 | 62.214241149928 | | 2015 | 61.699518413971 | | 2014 | 61.311605757289 | | 2013 | 60.928352080759 | | 2012 | 60.557899864509 | | 2011 | 60.304912008704 | | 2010 | 59.725139450866 | | 2009 | 59.219105816256 | | 2008 | 58.503457610192 | | 2007 | 57.928820818024 | | 2006 | 57.247705596934 | | 2005 | 56.392413682008 | | 2004 | 55.793774140021 | | 2003 | 55.309587475487 | | 2002 | 54.213809233824 | | 2001 | 53.729475440913 | | 2000 | 53.214812494311 | | 1999 | 52.238166946511 | | 1998 | 51.00856560104 | | 1997 | 51.441184850251 | | 1996 | 50.97989011822 | | 1995 | 50.853191615585 | | 1994 | 51.126886983387 | | 1993 | 50.40780404747 | | 1992 | 49.593582597598 | | 1991 | 49.693652987909 | | 1990 | 49.696346631758 | | 1989 | 49.644790834877 | | 1988 | 48.055420125193 | | 1987 | 48.519986827478 | | 1986 | 47.804248615693 | | 1985 | 46.962442941163 | | 1984 | 46.5626775836 | | 1983 | 46.744293186554 | | 1982 | 48.020106328546 | | 1981 | 47.93262689663 | | 1980 | 47.705338502258 | | 1979 | 47.359088090405 | | 1978 | 46.918300762002 | | 1977 | 46.689833615431 | | 1976 | 46.357580654502 | | 1975 | 45.6469308244 | | 1974 | 45.364368514357 | | 1973 | 45.273254776242 | | 1972 | 44.52803971946 | | 1971 | 44.731153214036 | | 1970 | 44.249287465021 | | 1969 | 43.914315695908 | | 1968 | 43.618345001737 | | 1967 | 43.236467248141 | | 1966 | 42.474126614486 | | 1965 | 42.640145337542 | | 1964 | 42.579931624779 | | 1963 | 41.926519218586 | | 1962 | 41.772609355582 | | 1961 | 41.433083736727 | | 1960 | 41.08512157075 |
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