Year | Value | 2015 | 31.62369863146 | 2014 | 28.989806791795 | 2013 | 28.104113632162 | 2012 | 23.399314402908 | 2011 | 24.774721116 | 2010 | 28.695795588269 | 2009 | 25.79573651267 | 2008 | 26.933709519804 | 2007 | 26.53847836876 | 2006 | 26.950883299277 | 2005 | 26.733909505334 | 2004 | 24.040756944971 | 2003 | 24.557915478295 | 2002 | 26.100097490596 | 2001 | 25.510896249492 | 2000 | 25.25379370802 | 1999 | 26.338478331441 | 1998 | 24.438149474978 | 1997 | 22.277524488887 | 1996 | 22.654751295439 | 1995 | 21.810456452981 | 1994 | 18.656645517812 | 1993 | 15.333272873608 | 1992 | 16.694424785886 | 1991 | 13.866451463062 | 1990 | 17.40153156544 | 1989 | 13.558321366535 | 1988 | 12.690119530568 | 1987 | 13.207463400419 | 1986 | 12.867329677194 | 1985 | 13.334733976484 | 1984 | 11.927792249149 | 1983 | 11.428964586326 | 1982 | 12.389444521219 | 1981 | 12.116620913406 | 1980 | 12.249083417255 | 1979 | 10.676372553801 | 1978 | 7.4658601744324 | 1977 | 9.9258722730248 | 1976 | 7.5616938626084 | 1975 | 7.3135501568668 | 1974 | 6.7141129938732 | 1973 | 14.732944989987 | 1972 | 12.875077517036 | 1971 | 11.97609575904 |
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