| Year | Value | | 2012 | 36.702295336413 | | 2011 | 4.7531638888566 | | 2010 | 4.3974138315007 | | 2009 | 2.9208971180536 | | 2008 | 15.745325221971 | | 2007 | 3.9077095044361 | | 2006 | 10.024110537757 | | 2005 | 7.2403493934853 | | 2004 | 4.4331413671984 | | 2003 | 5.7968294490584 | | 2002 | 0.1305052824174 | | 2001 | 2.9999999999999 | | 2000 | -3.8461538461538 | | 1999 | -3.7037037037036 | | 1998 | 0.79716563330392 | | 1997 | 1.8861113617909 | | 1996 | 8.2498900991551 | | 1995 | 7.9799578059069 | | 1994 | 15.328467153285 | | 1993 | 13.223140495868 | | 1992 | 11.009174311927 | | 1991 | 9 | | 1990 | 19.396867222954 | | 1989 | 11.399217221135 | | 1988 | 34.562211981567 | | 1987 | 59.48436770882 | | 1986 | 36.063492063492 | | 1985 | 17.252931323283 | | 1984 | 9.229518194755 | | 1983 | 6.1272923408846 | | 1982 | 14.303329223181 | | 1981 | 18.394160583942 | | 1980 | 19.296412399861 | | 1979 | 4.5520757465404 | | 1978 | 4.8091603053437 | | 1977 | 11.965811965812 | | 1976 | 11.428571428571 | | 1975 | 11.464968152866 | | 1974 | 15.528281750267 | | 1973 | 20.359666024406 | | 1972 | 2.0983606557383 | | 1971 | 5.6094182825485 | | 1970 | 4.6376811594198 | | 1969 | -1.988636363636 | | 1968 | 2.8487947406866 | | 1967 | 6.4541213063753 | | 1966 | 3.7933817594838 | | 1965 | -3.8789759503494 | | 1964 | 5.3965658217502 | | 1963 | 1.9166666666666 | | 1962 | -3.8461538461533 | | 1961 | 1.9588908815007 | | 1960 | 5.118909512761 |
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