| Year | Value | | 2022 | 3.2158980955966 | | 2021 | 1.2995084380596 | | 2020 | 1.2986353254456 | | 2019 | 1.2896084895423 | | 2018 | 1.3145229845788 | | 2017 | 1.3603812690899 | | 2016 | 1.4220461403292 | | 2015 | 1.4614846851916 | | 2014 | 1.4726708730575 | | 2013 | 1.439445356248 | | 2012 | 1.4086768870182 | | 2011 | 1.4315124488782 | | 2010 | 1.4132714774535 | | 2009 | 1.9824080569153 | | 2008 | 1.8729620961218 | | 2007 | 1.1438512334943 | | 2006 | 1.057671308665 | | 2005 | 0.88889804270202 | | 2004 | 0.69490948431126 | | 2003 | 0.33640891379325 | | 2002 | 0.0041255453945046 | | 2001 | 0.17006952632276 | | 2000 | 0.30020148669053 | | 1999 | 0.95511348167091 | | 1998 | -1.7284164484621 | | 1997 | -1.577523754061 | | 1996 | -1.5163215714792 | | 1995 | -2.0620398175728 | | 1994 | -1.4444255110241 | | 1993 | 0.35602362265798 | | 1992 | 0.076714450954582 | | 1991 | 0.63239182585153 | | 1990 | 0.60434266304362 | | 1989 | -1.1082702253713 | | 1988 | 2.2036473090175 | | 1987 | 2.2092587140209 | | 1986 | 1.9784034845985 | | 1985 | 1.7390302855065 | | 1984 | 1.7422553484021 | | 1983 | 1.7059069733837 | | 1982 | 1.6312810564795 | | 1981 | 1.5728725076557 | | 1980 | 1.5280150965453 | | 1979 | 1.4978146044212 | | 1978 | 1.5151709533384 | | 1977 | 1.4678600908765 | | 1976 | 1.4128149554318 | | 1975 | 1.4270026527231 | | 1974 | 1.4169058202479 | | 1973 | 1.4013938984731 | | 1972 | 1.3382763463225 | | 1971 | 1.4491195440431 | | 1970 | 1.8334312253056 | | 1969 | 2.2219668730002 | | 1968 | 2.4636602233544 | | 1967 | 2.5887349828849 | | 1966 | 2.7149992781959 | | 1965 | 2.8548266947074 | | 1964 | 3.0013095765307 | | 1963 | 3.1467021846368 | | 1962 | 3.2669535162312 | | 1961 | 3.3763004954302 |
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