| Year | Value | | 2021 | 61.796 | | 2020 | 62.265 | | 2019 | 62.872 | | 2018 | 62.614 | | 2017 | 62.037 | | 2016 | 61.777 | | 2015 | 61.211 | | 2014 | 60.679 | | 2013 | 60.327 | | 2012 | 59.791 | | 2011 | 59.059 | | 2010 | 58.439 | | 2009 | 57.651 | | 2008 | 56.718 | | 2007 | 56.138 | | 2006 | 55.509 | | 2005 | 54.373 | | 2004 | 54.349 | | 2003 | 53.627 | | 2002 | 53.35 | | 2001 | 52.825 | | 2000 | 52.561 | | 1999 | 51.239 | | 1998 | 51.36 | | 1997 | 50.016 | | 1996 | 51.071 | | 1995 | 50.953 | | 1994 | 50.112 | | 1993 | 50.146 | | 1992 | 49.896 | | 1991 | 49.44 | | 1990 | 49.004 | | 1989 | 48.577 | | 1988 | 48.174 | | 1987 | 47.648 | | 1986 | 47.384 | | 1985 | 47.012 | | 1984 | 46.776 | | 1983 | 46.575 | | 1982 | 46.346 | | 1981 | 46.114 | | 1980 | 45.75 | | 1979 | 45.391 | | 1978 | 45.08 | | 1977 | 44.815 | | 1976 | 44.475 | | 1975 | 44.142 | | 1974 | 43.849 | | 1973 | 43.24 | | 1972 | 42.856 | | 1971 | 42.593 | | 1970 | 42.244 | | 1969 | 41.968 | | 1968 | 41.588 | | 1967 | 41.259 | | 1966 | 40.923 | | 1965 | 40.615 | | 1964 | 40.208 | | 1963 | 39.9 | | 1962 | 39.915 | | 1961 | 39.631 | | 1960 | 39.439 |
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