Year | Value | 2021 | 23.956384151347 | 2020 | 24.638455246109 | 2019 | 24.514662777651 | 2018 | 24.17084372485 | 2017 | 23.629334654338 | 2016 | 23.064827501008 | 2015 | 23.197715462657 | 2014 | 23.161415317488 | 2013 | 23.210917872708 | 2012 | 22.530740079012 | 2011 | 21.81649645909 | 2010 | 21.952659489427 | 2009 | 20.701427684668 | 2008 | 22.005239964264 | 2007 | 22.122017554704 | 2006 | 22.57780884787 | 2005 | 22.295536849377 | 2004 | 22.162957103178 | 2003 | 22.116914193342 | 2002 | 22.567228586957 | 2001 | 23.374463658822 | 2000 | 23.39182393978 | 1999 | 23.631994027119 | 1998 | 23.026919230473 | 1997 | 21.100854981176 | 1996 | 20.385844541016 | 1995 | 19.46320734351 | 1994 | 19.084116977562 | 1993 | 18.384076566547 | 1992 | 18.466692568788 | 1991 | 18.918226150516 | 1990 | 18.734247316118 | 1989 | 18.906001441497 | 1988 | 19.212449948706 | 1987 | 19.870645838644 | 1986 | 19.659769088959 | 1985 | 19.651460577596 | 1984 | 19.56741342559 | 1983 | 19.444214649673 | 1982 | 19.600212561441 | 1981 | 19.36757321649 | 1980 | 19.291919152362 | 1979 | 18.831689706206 | 1978 | 18.257184035334 | 1977 | 18.240794449883 | 1976 | 18.839990135168 | 1975 | 17.7218201625 | 1974 | 18.873364252387 | 1973 | 17.844251105368 | 1972 | 18.67533827373 |
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