| Year | Value | | 2021 | 77.797290736099 | | 2020 | 78.26815055408 | | 2019 | 78.916166295836 | | 2018 | 78.720733054328 | | 2017 | 78.44615661659 | | 2016 | 78.193599376577 | | 2015 | 77.940525981448 | | 2014 | 77.723451968095 | | 2013 | 77.480692346304 | | 2012 | 77.188173538788 | | 2011 | 76.859626713137 | | 2010 | 76.554414762495 | | 2009 | 76.319831981437 | | 2008 | 75.890216445098 | | 2007 | 75.749383474917 | | 2006 | 75.459090180926 | | 2005 | 75.077877856875 | | 2004 | 74.589023030992 | | 2003 | 74.475364408033 | | 2002 | 74.20005262545 | | 2001 | 73.96709648937 | | 2000 | 73.306746391174 | | 1999 | 72.887355868681 | | 1998 | 72.863190310619 | | 1997 | 72.425289645525 | | 1996 | 72.074620623457 | | 1995 | 71.832592016788 | | 1994 | 71.444398803517 | | 1993 | 71.218769707451 | | 1992 | 70.845631533257 | | 1991 | 70.503516583395 | | 1990 | 70.471019456172 | | 1989 | 70.278109875082 | | 1988 | 70.01279910089 | | 1987 | 69.74510847864 | | 1986 | 69.407405108962 | | 1985 | 68.932804586031 | | 1984 | 68.576449869205 | | 1983 | 68.249625496718 | | 1982 | 67.82158219668 | | 1981 | 67.381562611088 | | 1980 | 66.891532587287 | | 1979 | 66.381534608593 | | 1978 | 65.876899453117 | | 1977 | 65.337552538431 | | 1976 | 64.689973188806 | | 1975 | 64.083770034501 | | 1974 | 63.524938978495 | | 1973 | 62.85358029543 | | 1972 | 62.132317509584 | | 1971 | 61.502600435425 | | 1970 | 60.761969953694 | | 1969 | 60.085359877159 | | 1968 | 59.645127060417 | | 1967 | 59.156984186484 | | 1966 | 58.541632741248 | | 1965 | 57.819144055691 | | 1964 | 57.645889560123 | | 1963 | 56.997535535261 | | 1962 | 56.487440717474 | | 1961 | 50.519495058713 | | 1960 | 46.0591438073 |
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