| Year | Value | | 2022 | 0.80807515055811 | | 2021 | 0.83481278803865 | | 2020 | 0.81769438551817 | | 2019 | 0.77908717743908 | | 2018 | 0.78945010772638 | | 2017 | 0.8197444733342 | | 2016 | 0.86386892284665 | | 2015 | 0.91195003624235 | | 2014 | 0.95639762384409 | | 2013 | 0.99764182582633 | | 2012 | 1.0413446078308 | | 2011 | 1.0955627133291 | | 2010 | 5.9397653658099 | | 2009 | 13.42292060267 | | 2008 | 17.399085995744 | | 2007 | 18.127983975525 | | 2006 | 13.48367209115 | | 2005 | 6.9557268979587 | | 2004 | 4.609526743863 | | 2003 | 4.8293426852932 | | 2002 | 5.0648725836099 | | 2001 | 5.3170759614716 | | 2000 | 5.5803870010153 | | 1999 | 5.8645145575703 | | 1998 | 6.1781885553755 | | 1997 | 6.521910678804 | | 1996 | 5.5438470982819 | | 1995 | 4.4081768696083 | | 1994 | 4.6463913593279 | | 1993 | 4.9348705828098 | | 1992 | 5.2306755586323 | | 1991 | 5.5396563994537 | | 1990 | 5.8690331846493 | | 1989 | 6.2260556904968 | | 1988 | 6.6150219295425 | | 1987 | 7.0456635498988 | | 1986 | 6.2628402406424 | | 1985 | 5.299493162126 | | 1984 | 5.5600883538787 | | 1983 | 5.7981806452141 | | 1982 | 5.9695786353261 | | 1981 | 8.1523561454267 | | 1980 | 10.996346821074 | | 1979 | 12.061285932197 | | 1978 | 13.029515158377 | | 1977 | 14.055088097246 | | 1976 | 12.244850487862 | | 1975 | 9.9447406446659 | | 1974 | 10.810504401758 | | 1973 | 11.808202995054 | | 1972 | 13.006834933573 | | 1971 | 14.475649961123 | | 1970 | 16.295474845348 | | 1969 | 17.039974365385 | | 1968 | 10.963445643016 | | 1967 | 4.7586890566977 | | 1966 | 4.8911535412569 | | 1965 | 5.0095699059129 | | 1964 | 5.150823122481 | | 1963 | 5.3163559504355 | | 1962 | 5.447405291216 | | 1961 | 5.5099391722853 |
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