| Year | Value | | 2022 | 5.2761672426285 | | 2021 | 4.0919518969286 | | 2020 | 2.4250065682182 | | 2019 | -1.1068634399419 | | 2018 | 0.35940903138068 | | 2017 | 0.6858810653046 | | 2016 | 0.72317845751322 | | 2015 | 1.2514995478148 | | 2014 | 0.44868207676614 | | 2013 | 2.5811703725294 | | 2012 | 1.304511199156 | | 2011 | 4.9124339505246 | | 2010 | 1.2264561213548 | | 2009 | 1.0195045773113 | | 2008 | 6.3085276915258 | | 2007 | 1.892006293496 | | 2006 | 2.4671914859692 | | 2005 | 3.8858303988648 | | 2004 | 1.4579883560074 | | 2003 | 3.2968074697421 | | 2002 | 3.0772648515743 | | 2001 | 4.3615291400726 | | 2000 | 2.5307751673799 | | 1999 | 0.70237580595596 | | 1998 | 4.6114475951538 | | 1997 | 4.020833333333 | | 1996 | 2.4808066918755 | | 1995 | 14.295069085195 | | 1994 | 26.081571994716 | | 1993 | 2.1647145397675 | | 1992 | 4.2313838286997 | | 1991 | 1.6833484986348 | | 1990 | 0.80587969827804 | | 1989 | 1.0495182379038 | | 1988 | 6.9306861720652 | | 1987 | 6.9433062653657 | | 1986 | 9.6829547311652 | | 1985 | 1.8638032715063 | | 1984 | 4.2847611036187 | | 1983 | 5.6404284334213 | | 1982 | 7.5831258964215 | | 1981 | 8.7992108330877 | | 1980 | 14.700981299787 | | 1979 | 16.342356573625 | | 1978 | 13.242986854593 | | 1977 | 27.421861509148 | | 1976 | 12.076640216957 | | 1975 | 11.444223967011 | | 1974 | 17.359388447065 | | 1973 | 11.102986669823 | | 1972 | 0.3103136988839 | | 1971 | 0.44374543627573 | | 1970 | 8.2051905431072 | | 1969 | 4.4502285422333 | | 1968 | 5.3504547886788 | | 1967 | 2.2918519534946 | | 1966 | 4.1913179840567 | | 1965 | 2.6111761263301 | | 1964 | 0.61819252274367 | | 1963 | 0.94346631046022 | | 1962 | -1.3412489012053 | | 1961 | 11.616492146899 |
|