| Year | Value | | 2023 | 10.39267855758 | | 2022 | 10.400493214424 | | 2021 | 10.408307871268 | | 2020 | 10.416122269613 | | 2019 | 10.423936926457 | | 2018 | 10.431751324803 | | 2017 | 10.439565981647 | | 2016 | 10.447380379992 | | 2015 | 10.455195036836 | | 2014 | 10.46300969368 | | 2013 | 10.470824092025 | | 2012 | 10.478638748869 | | 2011 | 10.856921287321 | | 2010 | 10.339925035543 | | 2009 | 10.598423161432 | | 2008 | 10.986170350265 | | 2007 | 10.339925035543 | | 2006 | 10.598423161432 | | 2005 | 10.081426909655 | | 2004 | 9.8229287837663 | | 2003 | 9.4351815949334 | | 2002 | 9.4351815949334 | | 2001 | 9.3059325319891 | | 2000 | 9.5671234328551 | | 1999 | 8.9299485588729 | | 1998 | 8.366299857826 | | 1997 | 8.4177192710353 | | 1996 | 8.5913007625695 | | 1995 | 8.1231221403645 | | 1994 | 8.1837117745896 | | 1993 | 7.4946260824609 | | 1992 | 7.2381840506656 | | 1991 | 7.8963197621817 | | 1990 | 7.747956830813 | | 1989 | 7.4515582267029 | | 1988 | 6.841566757141 | | 1987 | 6.6029740209384 | | 1986 | 6.8541760372237 | | 1985 | 6.5549936667959 | | 1984 | 6.4149820343802 | | 1983 | 6.2625250096937 | | 1982 | 5.8038441256301 | | 1981 | 5.5886687346517 | | 1980 | 5.2701631123174 | | 1979 | 5.0751296368101 | | 1978 | 4.9644303993796 | | 1977 | 4.9072795657232 | | 1976 | 4.6786759725992 | | 1975 | 4.5637192710353 |
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