| Year | Value | | 2021 | 11.521048719508 | | 2020 | 11.58862085276 | | 2019 | 11.673086019326 | | 2018 | 11.509348952467 | | 2017 | 11.342644739806 | | 2016 | 12.006758278892 | | 2015 | 11.897949988736 | | 2014 | 11.984681234512 | | 2013 | 11.901329128182 | | 2012 | 11.769542689795 | | 2011 | 11.293084027934 | | 2010 | 11.289704888488 | | 2009 | 11.545393106555 | | 2008 | 11.021078875793 | | 2007 | 10.916817769719 | | 2006 | 11.536718041704 | | 2005 | 11.480054397099 | | 2004 | 11.752039891206 | | 2003 | 11.38939256573 | | 2002 | 11.616047144152 | | 2001 | 11.582048957389 | | 2000 | 12.114687216682 | | 1999 | 12.09202175884 | | 1998 | 12.080689029918 | | 1997 | 12.024025385313 | | 1996 | 11.910698096102 | | 1995 | 12.624660018132 | | 1994 | 12.148685403445 | | 1993 | 12.352674524025 | | 1992 | 12.700589301904 | | 1991 | 11.450589301904 | | 1990 | 11.788304623753 | | 1989 | 13.030371713509 | | 1988 | 13.20262919311 | | 1987 | 13.10063463282 | | 1986 | 12.758386219402 | | 1985 | 12.667724388033 | | 1984 | 11.900498640073 | | 1983 | 12.896645512239 | | 1982 | 12.739120580236 | | 1981 | 12.665457842248 | | 1980 | 12.771985494107 | | 1979 | 12.749320036265 | | 1978 | 12.715321849501 | | 1977 | 12.669990933817 | | 1976 | 12.658658204896 | | 1975 | 12.635992747053 | | 1974 | 12.624660018132 | | 1973 | 12.579329102448 | | 1972 | 12.567996373527 | | 1971 | 12.522665457842 | | 1970 | 12.511332728921 | | 1969 | 12.466001813237 | | 1968 | 12.454669084315 | | 1967 | 12.432003626473 | | 1966 | 12.39800543971 | | 1965 | 12.375339981868 | | 1964 | 12.364007252947 | | 1963 | 12.318676337262 | | 1962 | 12.307343608341 | | 1961 | 12.284678150499 |
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