Year | Value | 2021 | 13.24 | 2020 | 13.333 | 2019 | 13.487 | 2018 | 13.488 | 2017 | 13.514 | 2016 | 13.525 | 2015 | 13.536 | 2014 | 13.45 | 2013 | 13.192 | 2012 | 12.957 | 2011 | 12.728 | 2010 | 12.706 | 2009 | 13.723 | 2008 | 13.983 | 2007 | 13.971 | 2006 | 14.207 | 2005 | 14.534 | 2004 | 15.051 | 2003 | 15.283 | 2002 | 16.067 | 2001 | 16.964 | 2000 | 17.44 | 1999 | 18.138 | 1998 | 18.718 | 1997 | 19.188 | 1996 | 20.004 | 1995 | 20.475 | 1994 | 20.661 | 1993 | 20.804 | 1992 | 20.834 | 1991 | 20.833 | 1990 | 20.515 | 1989 | 20.116 | 1988 | 20.255 | 1987 | 20.216 | 1986 | 20.495 | 1985 | 20.425 | 1984 | 20.364 | 1983 | 20.371 | 1982 | 20.536 | 1981 | 20.781 | 1980 | 20.622 | 1979 | 20.664 | 1978 | 20.449 | 1977 | 20.637 | 1976 | 21.641 | 1975 | 23.908 | 1974 | 25.408 | 1973 | 27.959 | 1972 | 33.352 | 1971 | 33.127 | 1970 | 35.036 | 1969 | 36.044 | 1968 | 36.953 | 1967 | 39.24 | 1966 | 36.62 | 1965 | 35.481 | 1964 | 35.561 | 1963 | 36.33 | 1962 | 34.269 | 1961 | 32.654 | 1960 | 35.194 |
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