| Year | Value | | 2019 | 8.8250669680456 | | 2018 | 6.8723286566294 | | 2017 | 4.5725365531752 | | 2016 | 6.9288252581608 | | 2015 | 9.4541718952602 | | 2014 | 4.953299184844 | | 2013 | 5.643038834255 | | 2012 | 1.4675832267468 | | 2011 | 5.0214601462073 | | 2010 | 7.7183819587361 | | 2009 | 1.4723431138565 | | 2008 | 26.799537193402 | | 2007 | 35.02459707177 | | 2006 | 19.996487335921 | | 2005 | 9.368618141967 | | 2004 | 4.5342137412969 | | 2003 | 36.589717532392 | | 2002 | 57.07451126217 | | 2001 | 21.101305376923 | | 2000 | 0.10916551466857 | | 1999 | 18.401043374161 | | 1998 | 51.487549750408 | | 1997 | 29.697232579153 | | 1996 | 16.275396637737 | | 1995 | 25.194712397285 | | 1994 | 24.098786075702 | | 1993 | 31.83160687276 | | 1992 | 21.913210400791 | | 1991 | 32.272038286642 | | 1990 | 17.62677503145 | | 1989 | 27.198526449089 | | 1988 | 16.042802180186 | | 1987 | 24.76 | | 1986 | 9.3254619000765 | | 1985 | 6.8075665576833 | | 1984 | 4.8463115476905 | | 1983 | 5.6500833634544 | | 1982 | 5.3047404053799 | | 1981 | 0.31844473326591 | | 1980 | 0.60815308389961 | | 1979 | 5.6722950288783 | | 1978 | -6.0447061257026 | | 1977 | -1.1566872425286 | | 1976 | 22.384401699229 | | 1975 | 31.655662934801 | | 1974 | 25.211661342204 | | 1973 | 25.19999999925 | | 1972 | 7.6426264800859 | | 1971 | 2.0879120879119 | | 1970 | -4.0084388175528 | | 1969 | -4.3390514632121 | | 1968 | 2.3760330578756 | | 1967 | 0.83333333229159 | | 1966 | 25.490196078432 | | 1965 | 17.692307692308 | | 1964 | 0.45941806891996 | | 1963 | -2.682563338341 | | 1962 | -1.6129032272725 | | 1961 | 0.1464128828721 | | 1960 | 7.3899371070349 |
|