| Year | Value | | 2021 | 1.5202891093559 | | 2020 | 1.5033321782505 | | 2019 | 1.525127741333 | | 2018 | 1.542244719375 | | 2017 | 1.55629652177 | | 2016 | 1.566499404273 | | 2015 | 1.5373015838372 | | 2014 | 1.5351507043134 | | 2013 | 1.5070844382682 | | 2012 | 1.5332647961293 | | 2011 | 1.5326062511896 | | 2010 | 1.5664573538302 | | 2009 | 1.558945625572 | | 2008 | 1.5663734282742 | | 2007 | 1.5164486819336 | | 2006 | 1.4945800786726 | | 2005 | 1.4678542825232 | | 2004 | 1.4558508027026 | | 2003 | 1.4322235400338 | | 2002 | 1.4208155397779 | | 2001 | 1.4226323868565 | | 2000 | 1.4409161498762 | | 1999 | 1.407532347891 | | 1998 | 1.405198203245 | | 1997 | 1.4154553073464 | | 1996 | 1.4130784896694 | | 1995 | 1.4150900224698 | | 1994 | 1.457719322327 | | 1993 | 1.5027514113226 | | 1992 | 1.545369542812 | | 1991 | 1.584116025788 | | 1990 | 1.6352245832189 | | 1989 | 1.6509578956165 | | 1988 | 1.6872124511362 | | 1987 | 1.6843604095273 | | 1986 | 1.7097317410243 | | 1985 | 1.7226260984785 | | 1984 | 1.7289675283121 | | 1983 | 1.7493787376987 | | 1982 | 1.794775266907 | | 1981 | 1.8184457512479 | | 1980 | 1.8691868877065 | | 1979 | 1.9028705957906 | | 1978 | 1.9390674454296 | | 1977 | 1.9897242282031 | | 1976 | 2.0563913775345 | | 1975 | 2.0942905825011 | | 1974 | 2.1583281545742 | | 1973 | 2.1509886375013 | | 1972 | 2.2255936224495 | | 1971 | 2.3122933081615 | | 1970 | 2.3538906953072 | | 1969 | 2.4448301332195 | | 1968 | 2.524138918915 | | 1967 | 2.5865753072717 | | 1966 | 2.5285548788376 | | 1965 | 2.5625314675779 | | 1964 | 2.6164909172282 | | 1963 | 2.5881311670414 | | 1962 | 2.5544717279672 | | 1961 | 2.5708505247596 | | 1960 | 2.5711864537911 |
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