| Year | Value | | 2021 | 2.8893383415198 | | 2020 | 2.8893383415198 | | 2019 | 2.8893383415198 | | 2018 | 2.8893383415198 | | 2017 | 2.8893383415198 | | 2016 | 2.8893383415198 | | 2015 | 2.8893383415198 | | 2014 | 2.8893383415198 | | 2013 | 2.8893383415198 | | 2012 | 2.8893383415198 | | 2011 | 2.8893383415198 | | 2010 | 2.9439147324152 | | 2009 | 2.9952807473755 | | 2008 | 3.0017014992456 | | 2007 | 3.0017014992456 | | 2006 | 3.0017014992456 | | 2005 | 3.0017014992456 | | 2004 | 3.0017014992456 | | 2003 | 3.0017014992456 | | 2002 | 3.0017014992456 | | 2001 | 3.0017014992456 | | 2000 | 3.0017014992456 | | 1999 | 3.0017014992456 | | 1998 | 3.0017014992456 | | 1997 | 3.0017014992456 | | 1996 | 3.0017014992456 | | 1995 | 3.0017014992456 | | 1994 | 3.0017014992456 | | 1993 | 3.0017014992456 | | 1992 | 3.0017014992456 | | 1991 | 3.0017014992456 | | 1990 | 3.0017014992456 | | 1989 | 3.0017014992456 | | 1988 | 3.0017014992456 | | 1987 | 3.0017014992456 | | 1986 | 3.0017014992456 | | 1985 | 3.0017014992456 | | 1984 | 3.0017014992456 | | 1983 | 3.0017014992456 | | 1982 | 3.0017014992456 | | 1981 | 3.0017014992456 | | 1980 | 3.0017014992456 | | 1979 | 2.9856496195705 | | 1978 | 2.9695977398953 | | 1977 | 2.9535458602202 | | 1976 | 2.9374939805451 | | 1975 | 2.92144210087 | | 1974 | 2.9053902211949 | | 1973 | 2.8893383415198 | | 1972 | 2.8732864618447 | | 1971 | 2.8572345821696 | | 1970 | 2.8411827024945 | | 1969 | 2.8251308228194 | | 1968 | 2.8090789431442 | | 1967 | 2.7930270634691 | | 1966 | 2.776975183794 | | 1965 | 2.7609233041189 | | 1964 | 2.7448714244438 | | 1963 | 2.7288195447687 | | 1962 | 2.7127676650936 | | 1961 | 2.6967157854185 |
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