Year | Value | 2014 | 22.015869961957 | 2013 | 18.697799081918 | 2012 | 18.049630978414 | 2011 | 17.960165368202 | 2010 | 17.774608838023 | 2009 | 19.293159885168 | 2008 | 20.728599945729 | 2007 | 20.995340675991 | 2006 | 19.380014935208 | 2005 | 19.49572622974 | 2004 | 27.713821001747 | 2003 | 24.554364468907 | 2002 | 24.9627355929 | 2001 | 24.888909445436 | 2000 | 23.307677116688 | 1999 | 22.032071811273 | 1998 | 20.656777386787 | 1997 | 22.452634781093 | 1996 | 17.861497823105 | 1995 | 17.769392593188 | 1994 | 4.3934003968116 | 1993 | 14.372123628118 | 1992 | 16.760314032275 | 1991 | 18.641827324132 | 1990 | 19.734221440692 | 1989 | 19.491306633768 | 1988 | 18.532316012937 | 1987 | 17.64753806809 | 1986 | 16.492506883176 | 1985 | 13.25604035191 | 1984 | 13.378462830285 | 1983 | 12.954622735502 | 1982 | 11.652034982529 | 1981 | 9.5170071165757 | 1980 | 9.8963499234266 | 1979 | 10.896807998269 | 1978 | 11.09294260163 | 1977 | 10.636794040434 | 1976 | 10.685680893772 | 1975 | 8.0923055027024 | 1974 | 8.2010532476545 | 1973 | 7.691867290611 | 1972 | 7.6837955375463 | 1971 | 8.4004929618659 |
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