Year | Value | 2022 | 19.026 | 2021 | 18.86 | 2020 | 18.713 | 2019 | 18.585 | 2018 | 18.476 | 2017 | 18.384 | 2016 | 18.311 | 2015 | 18.256 | 2014 | 18.218 | 2013 | 18.198 | 2012 | 18.196 | 2011 | 18.211 | 2010 | 18.226 | 2009 | 18.242 | 2008 | 18.257 | 2007 | 18.272 | 2006 | 18.288 | 2005 | 18.303 | 2004 | 18.319 | 2003 | 18.334 | 2002 | 18.349 | 2001 | 18.365 | 2000 | 18.38 | 1999 | 18.396 | 1998 | 18.411 | 1997 | 18.427 | 1996 | 18.442 | 1995 | 18.458 | 1994 | 18.473 | 1993 | 18.489 | 1992 | 18.504 | 1991 | 18.52 | 1990 | 18.535 | 1989 | 18.551 | 1988 | 18.566 | 1987 | 18.582 | 1986 | 18.597 | 1985 | 18.613 | 1984 | 18.629 | 1983 | 18.644 | 1982 | 18.66 | 1981 | 18.676 | 1980 | 18.607 | 1979 | 18.504 | 1978 | 18.401 | 1977 | 18.299 | 1976 | 18.198 | 1975 | 18.097 | 1974 | 17.996 | 1973 | 17.896 | 1972 | 17.796 | 1971 | 17.697 | 1970 | 17.598 | 1969 | 17.5 | 1968 | 17.402 | 1967 | 17.304 | 1966 | 17.207 | 1965 | 17.11 | 1964 | 17.014 | 1963 | 16.916 | 1962 | 16.753 | 1961 | 16.592 | 1960 | 16.431 |
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