| Year | Value | | 2021 | 11.856500815175 | | 2020 | 11.279229545359 | | 2019 | 9.902312737786 | | 2018 | 10.024782878127 | | 2017 | 10.000951390842 | | 2016 | 9.9635783221299 | | 2015 | 10.119999808582 | | 2014 | 9.837863998003 | | 2013 | 9.9241194373651 | | 2012 | 10.029893258325 | | 2011 | 9.9598263586954 | | 2010 | 10.136168189667 | | 2009 | 10.143679714158 | | 2008 | 10.312756314647 | | 2007 | 10.332236161792 | | 2006 | 10.387078210855 | | 2005 | 10.70335684815 | | 2004 | 10.539011461799 | | 2003 | 10.929323180881 | | 2002 | 10.81513893052 | | 2001 | 10.644056024343 | | 2000 | 10.692265874886 | | 1999 | 10.711122396875 | | 1998 | 10.520598091564 | | 1997 | 10.625883199728 | | 1996 | 10.814977868144 | | 1995 | 11.01531542093 | | 1994 | 11.059063619485 | | 1993 | 10.989013766327 | | 1992 | 10.43093834845 | | 1991 | 10.253822625844 | | 1990 | 10.149151292562 | | 1989 | 10.016936910154 | | 1988 | 10.078584752316 | | 1987 | 10.033898426554 | | 1986 | 10.094983454669 | | 1985 | 10.459267248443 | | 1984 | 10.405242351583 | | 1983 | 10.388845850926 | | 1982 | 10.2045291979 | | 1981 | 10.319397727304 | | 1980 | 10.463122632755 | | 1979 | 10.329225578455 | | 1978 | 10.382472157105 | | 1977 | 10.284785131889 | | 1976 | 10.391690025222 | | 1975 | 10.352855621547 | | 1974 | 10.186015651592 | | 1973 | 10.250713219705 | | 1972 | 10.183801322706 | | 1971 | 10.223512558625 | | 1970 | 10.218726725714 | | 1969 | 10.354253946428 | | 1968 | 10.132746090364 | | 1967 | 9.9199225501503 | | 1966 | 9.8494534988153 | | 1965 | 9.9170920924478 | | 1964 | 9.7409480170472 | | 1963 | 10.048415321629 | | 1962 | 10.175393879012 | | 1961 | 9.9443202271568 | | 1960 | 10.061763947056 |
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