| Year | Value | | 2015 | 30.536533777595 | | 2014 | -18.825317099686 | | 2013 | -27.807504619409 | | 2012 | -29.0354946769 | | 2011 | -32.687859980404 | | 2010 | -31.726740599623 | | 2009 | -33.298948185533 | | 2008 | -40.104643161893 | | 2007 | -44.076374148685 | | 2006 | -49.512671748572 | | 2005 | -52.980757783043 | | 2004 | -52.751010959893 | | 2003 | -53.235641348257 | | 2002 | -48.679176339247 | | 2001 | -52.87937997371 | | 2000 | -55.782572866265 | | 1999 | -53.810871695218 | | 1998 | -61.050595510664 | | 1997 | -63.249315961285 | | 1996 | -65.782348680989 | | 1995 | -66.349906999608 | | 1994 | -67.748165046199 | | 1993 | -72.689826695122 | | 1992 | -73.952473312941 | | 1991 | -77.462710919495 | | 1990 | -70.213004537719 | | 1989 | -62.350716132087 | | 1988 | -62.152381570455 | | 1987 | -57.672781828497 | | 1986 | -63.69147146531 | | 1985 | -59.677229003693 | | 1984 | -70.53718811882 | | 1983 | -73.307090772778 | | 1982 | -81.657755810138 | | 1981 | -104.52426386257 | | 1980 | -116.25137564156 | | 1979 | -133.33249228284 | | 1978 | -144.77016253583 | | 1977 | -159.75451232286 | | 1976 | -162.73144479633 | | 1975 | -148.99196968586 | | 1974 | -180.27488211884 | | 1973 | -190.58336079113 | | 1972 | -178.03327285814 | | 1971 | -169.15405975902 | | 1970 | 23.184991572491 | | 1969 | 19.435914726701 | | 1968 | 18.088274208953 | | 1967 | 16.256700210398 | | 1966 | 19.350595763956 | | 1965 | 18.820090522769 | | 1964 | 19.243570633854 | | 1963 | 18.026198345036 | | 1962 | 17.941880543195 | | 1961 | 12.586700771082 | | 1960 | 12.335653942187 |
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