| Year | Value | | 2022 | 2.0240363099997 | | 2021 | 2.0457148779533 | | 2020 | 2.0311117103548 | | 2019 | 1.9892527477704 | | 2018 | 2.020537287771 | | 2017 | 2.0436198988038 | | 2016 | 2.0818057250025 | | 2015 | 2.1362942381113 | | 2014 | 2.1913910559234 | | 2013 | 2.1632674727572 | | 2012 | 1.8223085624557 | | 2011 | 1.438339132555 | | 2010 | 1.253649854212 | | 2009 | 1.026265007174 | | 2008 | 0.79820702379433 | | 2007 | 0.96911875029836 | | 2006 | 0.86122261991742 | | 2005 | 0.5238506086351 | | 2004 | 0.70185559551988 | | 2003 | 0.75796049675258 | | 2002 | 0.6165667783866 | | 2001 | 0.64266296995523 | | 2000 | 1.0039687523875 | | 1999 | 1.4450396727921 | | 1998 | 1.6234035319201 | | 1997 | 1.6346887957256 | | 1996 | 1.6609459898687 | | 1995 | 1.2396558544075 | | 1994 | 0.58813723657238 | | 1993 | 1.4313922436179 | | 1992 | 2.5091190776518 | | 1991 | 2.5760331408983 | | 1990 | 2.6809601314278 | | 1989 | 2.8598991044898 | | 1988 | 3.0910610347876 | | 1987 | 3.2252020123873 | | 1986 | 3.310659933343 | | 1985 | 3.4171104984426 | | 1984 | 3.5412650731035 | | 1983 | 3.8030602954139 | | 1982 | 3.8845066843928 | | 1981 | 6.275565521386 | | 1980 | 5.7523507255275 | | 1979 | 1.6127957665176 | | 1978 | 1.4813697930267 | | 1977 | 2.5847358429905 | | 1976 | 3.0894138949128 | | 1975 | 3.2259983002147 | | 1974 | 3.2856609954213 | | 1973 | 3.1992259557939 | | 1972 | 3.1099216916039 | | 1971 | 3.0382768609508 | | 1970 | 3.0987888842536 | | 1969 | 3.1786743650614 | | 1968 | 3.1527890134691 | | 1967 | 3.1357606012597 | | 1966 | 3.1296276703698 | | 1965 | 3.1248285390059 | | 1964 | 3.1198783392385 | | 1963 | 3.1154083117767 | | 1962 | 3.1053195206129 | | 1961 | 3.0948653696492 |
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