| Year | Value | | 2021 | 12.003434371311 | | 2020 | 12.003434371311 | | 2019 | 11.940573110712 | | 2018 | 11.949772319581 | | 2017 | 11.80411817917 | | 2016 | 11.85011422351 | | 2015 | 11.905309476718 | | 2014 | 11.914508685586 | | 2013 | 11.935973506279 | | 2012 | 11.943639513669 | | 2011 | 11.945172715146 | | 2010 | 11.948239118102 | | 2009 | 11.948239118102 | | 2008 | 11.949772319581 | | 2007 | 11.949772319581 | | 2006 | 11.949772319581 | | 2005 | 11.966637535839 | | 2004 | 11.983502752097 | | 2003 | 11.916041887064 | | 2002 | 11.771920948132 | | 2001 | 11.779586955522 | | 2000 | 11.779586955522 | | 1999 | 11.733590911182 | | 1998 | 11.893043864894 | | 1997 | 11.782653358478 | | 1996 | 11.724391702314 | | 1995 | 11.733590911182 | | 1994 | 11.810250985082 | | 1993 | 11.995768363921 | | 1992 | 12.127623691029 | | 1991 | 12.127623691029 | | 1990 | 12.127623691029 | | 1989 | 12.127623691029 | | 1988 | 12.127623691029 | | 1987 | 12.127623691029 | | 1986 | 12.127623691029 | | 1985 | 12.127623691029 | | 1984 | 12.127623691029 | | 1983 | 12.127623691029 | | 1982 | 12.127623691029 | | 1981 | 12.127623691029 | | 1980 | 12.127623691029 | | 1979 | 12.127623691029 | | 1978 | 12.127623691029 | | 1977 | 12.127623691029 | | 1976 | 12.127623691029 | | 1975 | 12.127623691029 | | 1974 | 12.127623691029 | | 1973 | 12.127623691029 | | 1972 | 12.127623691029 | | 1971 | 12.112291676249 | | 1970 | 12.066295631909 | | 1969 | 12.050963617129 | | 1968 | 12.026432393481 | | 1967 | 12.026432393481 | | 1966 | 12.012633580179 | | 1965 | 11.958971528449 | | 1964 | 11.958971528449 | | 1963 | 11.882311454548 | | 1962 | 11.805651380648 | | 1961 | 11.728991306748 |
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