| Year | Value | | 2022 | 5.8211581121395 | | 2021 | 3.9271802210033 | | 2020 | 2.3931623931624 | | 2019 | 2.392065344224 | | 2018 | 5.3093466162771 | | 2017 | 2.8531877259095 | | 2016 | 1.2536988008098 | | 2015 | 0.67419253684541 | | 2014 | 3.5978234386421 | | 2013 | 2.582687661418 | | 2012 | 3.026963911248 | | 2011 | 4.7184170471842 | | 2010 | 3.7898363479759 | | 2009 | 4.2190305206463 | | 2008 | 8.2604470359573 | | 2007 | 2.9 | | 2006 | 5.4852320675105 | | 2005 | 6.5168539325843 | | 2004 | 4.8292108362779 | | 2003 | 2.2891566265061 | | 2002 | 2.7227722772277 | | 2001 | 5.3455019556714 | | 2000 | 3.9771250324928 | | 1999 | 5.9390490178081 | | 1998 | 9.2349343226712 | | 1997 | 5.590259396506 | | 1996 | 7.4761037778791 | | 1995 | 6.8319961098953 | | 1994 | 10.386473429952 | | 1993 | 6.7163110410997 | | 1992 | 8.6510035786527 | | 1991 | 19.261458526628 | | 1990 | 12.177352206495 | | 1989 | 12.242990654205 | | 1988 | 13.860069167332 | | 1987 | 4.0697674418602 | | 1986 | 1.1481377765334 | | 1985 | 23.103107180389 | | 1984 | 50.33897563745 | | 1983 | 10.029356562048 | | 1982 | 10.221727137689 | | 1981 | 13.082598524168 | | 1980 | 18.200510493851 | | 1979 | 17.53333333275 | | 1978 | 7.3345259391769 | | 1977 | 9.8987515973657 | | 1976 | 9.1992271361101 | | 1975 | 6.7614027045608 | | 1974 | 34.163591635916 | | 1973 | 16.580032263846 | | 1972 | 8.2040341349883 | | 1971 | 21.403343536614 | | 1970 | 14.381461675733 | | 1969 | 1.9555103228538 | | 1968 | 2.3588064589059 | | 1967 | 6.2539531939773 | | 1966 | 5.3999999996807 | | 1965 | 2.5641025642845 | | 1964 | 8.1830790570033 | | 1963 | 5.6255493700882 | | 1962 | 5.7966522010138 | | 1961 | 1.5956330045272 | | 1960 | 4.1548217798216 |
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