| Year | Value | | 2021 | 4.387 | | 2020 | 4.454 | | 2019 | 4.517 | | 2018 | 4.584 | | 2017 | 4.622 | | 2016 | 4.683 | | 2015 | 4.781 | | 2014 | 4.905 | | 2013 | 4.96 | | 2012 | 5.005 | | 2011 | 5.039 | | 2010 | 5.064 | | 2009 | 5.081 | | 2008 | 5.051 | | 2007 | 5.11 | | 2006 | 5.198 | | 2005 | 5.186 | | 2004 | 5.184 | | 2003 | 5.252 | | 2002 | 5.311 | | 2001 | 5.412 | | 2000 | 5.498 | | 1999 | 5.573 | | 1998 | 5.581 | | 1997 | 5.639 | | 1996 | 5.723 | | 1995 | 5.819 | | 1994 | 5.915 | | 1993 | 6.049 | | 1992 | 6.149 | | 1991 | 6.267 | | 1990 | 6.396 | | 1989 | 6.479 | | 1988 | 6.577 | | 1987 | 6.785 | | 1986 | 6.902 | | 1985 | 7.013 | | 1984 | 7.111 | | 1983 | 7.189 | | 1982 | 7.245 | | 1981 | 7.279 | | 1980 | 7.292 | | 1979 | 7.29 | | 1978 | 7.279 | | 1977 | 7.268 | | 1976 | 7.258 | | 1975 | 7.252 | | 1974 | 7.252 | | 1973 | 7.255 | | 1972 | 7.258 | | 1971 | 7.261 | | 1970 | 7.262 | | 1969 | 7.259 | | 1968 | 7.251 | | 1967 | 7.237 | | 1966 | 7.217 | | 1965 | 7.19 | | 1964 | 7.157 | | 1963 | 7.12 | | 1962 | 7.079 | | 1961 | 7.038 | | 1960 | 6.996 |
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