| Year | Value | | 2021 | 2.031 | | 2020 | 2.051 | | 2019 | 2.109 | | 2018 | 2.177 | | 2017 | 2.2 | | 2016 | 2.273 | | 2015 | 2.287 | | 2014 | 2.306 | | 2013 | 2.406 | | 2012 | 2.467 | | 2011 | 2.536 | | 2010 | 2.603 | | 2009 | 2.673 | | 2008 | 2.718 | | 2007 | 2.784 | | 2006 | 2.864 | | 2005 | 2.958 | | 2004 | 3.046 | | 2003 | 3.122 | | 2002 | 3.217 | | 2001 | 3.303 | | 2000 | 3.35 | | 1999 | 3.383 | | 1998 | 3.446 | | 1997 | 3.514 | | 1996 | 3.582 | | 1995 | 3.651 | | 1994 | 3.723 | | 1993 | 3.799 | | 1992 | 3.877 | | 1991 | 3.959 | | 1990 | 4.045 | | 1989 | 4.132 | | 1988 | 4.222 | | 1987 | 4.311 | | 1986 | 4.399 | | 1985 | 4.432 | | 1984 | 4.516 | | 1983 | 4.565 | | 1982 | 4.62 | | 1981 | 4.698 | | 1980 | 4.775 | | 1979 | 4.808 | | 1978 | 4.888 | | 1977 | 5.007 | | 1976 | 5.13 | | 1975 | 5.195 | | 1974 | 5.325 | | 1973 | 5.402 | | 1972 | 5.482 | | 1971 | 5.565 | | 1970 | 5.624 | | 1969 | 5.684 | | 1968 | 5.76 | | 1967 | 5.825 | | 1966 | 5.881 | | 1965 | 5.941 | | 1964 | 5.979 | | 1963 | 5.969 | | 1962 | 5.953 | | 1961 | 5.937 | | 1960 | 5.921 |
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