| Year | Value | | 2021 | 11.548482471298 | | 2020 | 11.536166870773 | | 2019 | 11.48634041255 | | 2018 | 11.514463890017 | | 2017 | 11.52495844901 | | 2016 | 11.526808515482 | | 2015 | 11.510631268512 | | 2014 | 11.475902498338 | | 2013 | 11.48552231729 | | 2012 | 11.476556724508 | | 2011 | 11.466920191741 | | 2010 | 11.454514459154 | | 2009 | 11.43831532794 | | 2008 | 11.421286844794 | | 2007 | 11.440014135739 | | 2006 | 11.42005108089 | | 2005 | 11.376243232323 | | 2004 | 11.348630134654 | | 2003 | 11.327070614929 | | 2002 | 11.290139377154 | | 2001 | 11.279760118474 | | 2000 | 11.259705546736 | | 1999 | 11.304427660583 | | 1998 | 11.278303271259 | | 1997 | 11.278465506392 | | 1996 | 11.238340738889 | | 1995 | 11.265779739928 | | 1994 | 11.268635715985 | | 1993 | 11.299173149677 | | 1992 | 11.34065168775 | | 1991 | 11.738176768059 | | 1990 | 11.713873349513 | | 1989 | 11.716184446608 | | 1988 | 11.668460552103 | | 1987 | 11.670266157226 | | 1986 | 11.608231263812 | | 1985 | 11.610267774182 | | 1984 | 11.401797659158 | | 1983 | 11.19107160493 | | 1982 | 11.107836726823 | | 1981 | 10.953186464081 | | 1980 | 10.907566603215 | | 1979 | 10.886909051498 | | 1978 | 10.810056271 | | 1977 | 10.710460127261 | | 1976 | 10.639818912297 | | 1975 | 10.573487723152 | | 1974 | 10.545445120871 | | 1973 | 10.507646218968 | | 1972 | 10.430501203494 | | 1971 | 10.33884633742 | | 1970 | 10.334919728438 | | 1969 | 10.307160152521 | | 1968 | 10.306120586846 | | 1967 | 10.256833251248 | | 1966 | 10.208104917515 | | 1965 | 10.161498943216 | | 1964 | 10.106063807254 | | 1963 | 10.060270799807 | | 1962 | 9.9801607951318 | | 1961 | 9.9409032463428 |
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