| Year | Value | | 2021 | 11.202796325043 | | 2020 | 11.186482137057 | | 2019 | 11.139851408205 | | 2018 | 11.158274787393 | | 2017 | 11.155239857721 | | 2016 | 11.1402153678 | | 2015 | 11.108671658577 | | 2014 | 11.07058253028 | | 2013 | 11.066809779762 | | 2012 | 11.035672465996 | | 2011 | 10.988036840351 | | 2010 | 10.94956604644 | | 2009 | 10.905026854688 | | 2008 | 10.859162521121 | | 2007 | 10.866818156179 | | 2006 | 10.826019646943 | | 2005 | 10.775473026484 | | 2004 | 10.723215505788 | | 2003 | 10.70871321598 | | 2002 | 10.62644690429 | | 2001 | 10.602400748208 | | 2000 | 10.574435677815 | | 1999 | 10.609125038665 | | 1998 | 10.586652699411 | | 1997 | 10.582648512904 | | 1996 | 10.540476940547 | | 1995 | 10.543758863461 | | 1994 | 10.518055980203 | | 1993 | 10.542853990164 | | 1992 | 10.548342448879 | | 1991 | 10.617663410355 | | 1990 | 10.581322654767 | | 1989 | 10.559519013179 | | 1988 | 10.520545698439 | | 1987 | 10.518591227446 | | 1986 | 10.474244718563 | | 1985 | 10.473671713653 | | 1984 | 10.305233547815 | | 1983 | 10.137791697592 | | 1982 | 10.068289357667 | | 1981 | 9.9405745213607 | | 1980 | 9.9073180475338 | | 1979 | 9.8878291031943 | | 1978 | 9.8206811031809 | | 1977 | 9.7335895112092 | | 1976 | 9.6747146427161 | | 1975 | 9.6121147909686 | | 1974 | 9.5896958423828 | | 1973 | 9.5662373653884 | | 1972 | 9.5054414452667 | | 1971 | 9.423147246549 | | 1970 | 9.4110337242321 | | 1969 | 9.3992779271309 | | 1968 | 9.3863380178078 | | 1967 | 9.3347445765881 | | 1966 | 9.2918794914409 | | 1965 | 9.2566666636724 | | 1964 | 9.2034070859418 | | 1963 | 9.1545066057143 | | 1962 | 9.081654264803 | | 1961 | 9.0376525321414 |
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