| Year | Value | | 2022 | 1.1777200973033 | | 2021 | 1.3815377379196 | | 2020 | 1.4205779099733 | | 2019 | 1.3647137464926 | | 2018 | 1.3435578410394 | | 2017 | 1.6755565135634 | | 2016 | 1.491549688046 | | 2015 | 1.7614835929375 | | 2014 | 1.5875763810985 | | 2013 | 1.7216025753292 | | 2012 | 1.3514017613208 | | 2011 | 1.4882329168936 | | 2010 | 1.5653798807818 | | 2009 | 1.9152987562087 | | 2008 | 1.7285608001368 | | 2007 | 1.4997013079913 | | 2006 | 1.3901661517264 | | 2005 | 1.3865656674433 | | 2004 | 1.5223171321896 | | 2003 | 1.3247463104085 | | 2002 | 1.5336618420578 | | 2001 | 1.5631722812714 | | 2000 | 1.53306641516 | | 1999 | 2.105156337892 | | 1998 | 0.95121760476294 | | 1997 | 0.8789553932426 | | 1996 | 0.80865970926076 | | 1995 | 1.0012334102531 | | 1994 | 1.4868084361686 | | 1993 | 2.4542897136074 | | 1992 | 1.7057040595541 | | 1991 | 2.5504286326308 | | 1987 | 2.8817870608152 | | 1986 | 1.8589728723444 | | 1985 | 1.63605853333 | | 1984 | 1.9589230444502 | | 1983 | 2.2726324633622 | | 1982 | 2.2781847335618 | | 1981 | 3.8275293705349 | | 1980 | 3.6469037761171 | | 1979 | 4.1669318398192 | | 1978 | 4.7709458689251 | | 1977 | 5.29674064816 | | 1976 | 5.5789369178889 | | 1975 | 6.2703574342392 | | 1974 | 5.0342052595809 | | 1973 | 4.6982528078609 | | 1972 | 4.6801032705023 | | 1971 | 4.310681849175 | | 1970 | 4.5241245243228 | | 1969 | 6.4839268078789 | | 1968 | 5.4110319386011 | | 1966 | 1.4495201806725 | | 1965 | 1.6543616715182 | | 1964 | 2.4843160583735 | | 1963 | 2.2308610148235 | | 1962 | 2.2675459022842 |
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