| Year | Value | | 2017 | 0.173580024 | | 2016 | 0.17480365 | | 2015 | 0.17273088 | | 2014 | 0.176256 | | 2013 | 0.145272 | | 2012 | 0.12010357108094 | | 2011 | 0.092123114639636 | | 2010 | 0.073942936 | | 2009 | 0.489 | | 2008 | 0.586 | | 2007 | 0.568 | | 2006 | 0.561 | | 2005 | 0.571 | | 2004 | 0.59 | | 2003 | 1.644 | | 2002 | 1.637 | | 2001 | 1.764 | | 2000 | 1.598 | | 1999 | 1.5 | | 1998 | 1.1000000238 | | 1997 | 0.5 | | 1996 | 0.400000006 | | 1995 | 0.400000006 | | 1994 | 0.400000006 | | 1993 | 0.400000006 | | 1992 | 0.3000000119 | | 1991 | 0.3000000119 | | 1990 | 0.3000000119 | | 1989 | 0.3000000119 | | 1988 | 0.3000000119 | | 1987 | 0.3000000119 | | 1986 | 0.3000000119 | | 1985 | 0.200000003 | | 1984 | 0.200000003 | | 1983 | 0.3000000119 | | 1982 | 0.200000003 | | 1981 | 3.5 | | 1980 | 3 | | 1979 | 3 | | 1978 | 2.0999999046 | | 1977 | 1.8999999762 | | 1976 | 1.8999999762 | | 1975 | 1.6000000238 |
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