Year | Value | 2017 | 31.580909671124 | 2016 | 29.712779129546 | 2015 | 31.613504819584 | 2014 | 27.455889458228 | 2013 | 30.444351851649 | 2012 | 29.447001585468 | 2011 | 27.459386232476 | 2010 | 22.640022035654 | 2009 | 27.204833626189 | 2008 | 27.93297709229 | 2007 | 26.487079193081 | 2006 | 19.847338940415 | 2005 | 17.208219841346 | 2004 | 15.060443710693 | 2003 | 17.906200280164 | 2002 | 18.674080619161 | 2001 | 19.582407422472 | 2000 | 21.903624925482 | 1999 | 18.373585835256 | 1998 | 20.267822179809 | 1997 | 25.948260391749 | 1996 | 24.979950344937 | 1995 | 22.347580254251 | 1994 | 23.016147348692 | 1993 | 19.85789970229 | 1992 | 17.100050399525 | 1991 | 11.789132943271 | 1990 | 15.845371914404 | 1989 | 2.336257591447 | 1988 | 15.88815371406 | 1987 | 23.246611107314 | 1986 | 14.449212368257 | 1985 | 15.582548886099 | 1984 | 12.478012253187 | 1983 | 25.048739769983 | 1982 | 27.98406154258 | 1981 | 18.850841510973 | 1980 | 22.763379550066 | 1979 | 27.309197150878 | 1978 | 30.425395922885 | 1977 | 28.080911471616 |
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