Year | Value | 2019 | 22.706258281507 | 2018 | 22.260498001343 | 2017 | 21.560716089125 | 2016 | 21.206674850766 | 2015 | 18.231482244014 | 2014 | 14.179066174883 | 2013 | 11.94109447783 | 2012 | 11.005683010566 | 2011 | 8.583871553993 | 2010 | 13.419187531558 | 2009 | 12.952563295721 | 2008 | 6.19581054463 | 2007 | 15.552473032591 | 2006 | 17.436268706757 | 2005 | 15.025248651222 | 2004 | 20.725958973469 | 2003 | 17.873967048062 | 2002 | 15.970102933727 | 2001 | 17.361083181808 | 2000 | 16.759702848699 | 1999 | 18.647047758702 | 1998 | 18.632179953421 | 1997 | 21.851501579225 | 1996 | 23.724574094688 | 1995 | 23.751917567533 | 1994 | 25.923056759976 | 1993 | 34.152549984527 | 1992 | 26.074815810518 | 1991 | 18.405851814325 | 1990 | 19.041961513629 | 1989 | 21.278857196227 | 1988 | 24.343854861281 | 1987 | 16.261583464756 | 1986 | 15.899106307874 | 1985 | 13.060942567056 | 1984 | 11.795216380702 | 1983 | 14.004859592836 | 1982 | 10.277554747076 | 1981 | 11.413949428103 | 1980 | 12.519710716306 | 1979 | 16.146448194967 | 1978 | 14.923958644406 | 1977 | 12.256712326328 | 1976 | 8.4071630102048 |
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