| Year | Value | | 2021 | 4.0611510791367 | | 2020 | 4.0611510791367 | | 2019 | 4.0611510791367 | | 2018 | 4.4424460431655 | | 2017 | 6.8561151079137 | | 2016 | 9.1024734982332 | | 2015 | 11.469964664311 | | 2014 | 9.8939929328622 | | 2013 | 8.4805653710247 | | 2012 | 7.0671378091873 | | 2011 | 5.6537102473498 | | 2010 | 4.2402826855124 | | 2009 | 2.791519434629 | | 2008 | 3.1802120141343 | | 2007 | 3.5335689045936 | | 2006 | 3.6749116607774 | | 2005 | 3.886925795053 | | 2004 | 4.2402826855124 | | 2003 | 4.5936395759717 | | 2002 | 4.5936395759717 | | 2001 | 4.9469964664311 | | 2000 | 4.9469964664311 | | 1999 | 5.7597173144876 | | 1998 | 6.0070671378092 | | 1997 | 6.0070671378092 | | 1996 | 6.0070671378092 | | 1995 | 6.0070671378092 | | 1994 | 6.0070671378092 | | 1993 | 6.0070671378092 | | 1992 | 6.0070671378092 | | 1991 | 6.7137809187279 | | 1990 | 6.7137809187279 | | 1989 | 6.5371024734982 | | 1988 | 6.3604240282686 | | 1987 | 6.2544169611307 | | 1986 | 6.1484098939929 | | 1985 | 6.0070671378092 | | 1984 | 6.0070671378092 | | 1983 | 5.8657243816254 | | 1982 | 5.6537102473498 | | 1981 | 5.6537102473498 | | 1980 | 5.6537102473498 | | 1979 | 5.4770318021201 | | 1978 | 5.3003533568905 | | 1977 | 5.3003533568905 | | 1976 | 5.3003533568905 | | 1975 | 4.9469964664311 | | 1974 | 4.5936395759717 | | 1973 | 4.5936395759717 | | 1972 | 4.5936395759717 | | 1971 | 4.5936395759717 | | 1970 | 4.416961130742 | | 1969 | 4.2402826855124 | | 1968 | 4.2402826855124 | | 1967 | 3.886925795053 | | 1966 | 3.886925795053 | | 1965 | 3.886925795053 | | 1964 | 3.886925795053 | | 1963 | 3.886925795053 | | 1962 | 3.886925795053 | | 1961 | 3.5335689045936 |
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