Year | Value | 2015 | 20.51837903474 | 2014 | 5.0933676086913 | 2013 | 8.1346159372491 | 2012 | 9.7972365663669 | 2011 | 11.821435598408 | 2010 | 15.102415937633 | 2009 | 14.535943992121 | 2008 | 15.561918117303 | 2007 | 17.743780668314 | 2006 | 16.911829320148 | 2005 | 17.233230497604 | 2004 | 17.538302014891 | 2003 | 17.417319532469 | 2002 | 17.692379383887 | 2001 | 15.849438664714 | 2000 | 16.351551335619 | 1999 | 16.516267415704 | 1998 | 13.943235771647 | 1997 | 14.048663778976 | 1996 | 13.985485300458 | 1995 | 13.310526398969 | 1994 | 13.069616355948 | 1993 | 13.732533687826 | 1992 | 13.034903542282 | 1991 | 14.125164628982 | 1990 | 15.218567153909 | 1989 | 16.57522854275 | 1988 | 15.928353738929 | 1987 | 15.513012123495 | 1986 | 13.851660083978 | 1985 | 15.811768708472 | 1984 | 14.314677800876 | 1983 | 15.324389537689 | 1982 | 13.14014739966 | 1981 | 10.679687427854 | 1980 | 12.160965416176 | 1979 | 14.764810741137 | 1978 | 18.075448886118 | 1977 | 16.052828945036 | 1976 | 16.87767890121 | 1975 | 15.190058377619 | 1974 | 15.097432143218 | 1973 | 16.359268941562 | 1972 | 15.389909996926 | 1971 | 15.646038350154 | 1970 | 29.53654849199 | 1969 | 29.386582329524 | 1968 | 26.723569716729 | 1967 | 24.737427882794 | 1966 | 24.552189197951 | 1965 | 23.720467957654 | 1964 | 21.97776468696 | 1963 | 21.158927151814 | 1962 | 19.029128631844 | 1961 | 17.665105383401 | 1960 | 16.741830222416 |
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