| Year | Value | | 2022 | 1.5554828682919 | | 2021 | 1.5750779313448 | | 2020 | 1.6537596305768 | | 2019 | 1.5707430798302 | | 2018 | 1.5634817837514 | | 2017 | 1.5794245240222 | | 2016 | 1.6094275206157 | | 2015 | 1.6363036549382 | | 2014 | 1.5850752502594 | | 2013 | 1.5451106733436 | | 2012 | 1.4953624960114 | | 2011 | 1.470349886653 | | 2010 | 1.4854677863057 | | 2009 | 1.5740082579106 | | 2008 | 1.4720858718578 | | 2007 | 1.47871072951 | | 2006 | 1.4760515231275 | | 2005 | 1.4490230774422 | | 2004 | 1.4343253212626 | | 2003 | 1.4540782731711 | | 2002 | 1.4536720039477 | | 2001 | 1.4160343973235 | | 2000 | 1.3502033014225 | | 1999 | 1.4078225426429 | | 1998 | 1.4077768934069 | | 1997 | 1.4425925544529 | | 1996 | 1.431705738402 | | 1995 | 1.3980893912222 | | 1994 | 1.4337550370495 | | 1993 | 1.49809365079 | | 1992 | 1.5750181000349 | | 1991 | 1.5609749459962 | | 1990 | 1.6036908727663 | | 1989 | 1.6021031696998 | | 1988 | 1.473460467369 | | 1987 | 1.5056660397104 | | 1986 | 1.5277585316213 | | 1985 | 1.7135669659935 | | 1984 | 1.7228205163319 | | 1983 | 1.7643101927976 | | 1982 | 1.8509158097176 | | 1981 | 1.7639667545324 | | 1980 | 1.7412153977687 | | 1979 | 1.650612758192 | | 1978 | 1.5782841179391 | | 1977 | 1.6693762933792 | | 1976 | 1.6592898149746 | | 1975 | 1.4561543471392 | | 1974 | 1.4182807476216 | | 1973 | 1.2477061097538 | | 1972 | 1.3723756434761 | | 1971 | 1.4326793148105 | | 1970 | 1.3912715828186 | | 1969 | 1.5052739084244 | | 1968 | 1.603627166242 | | 1967 | 1.6539663738093 | | 1963 | 1.5721389575666 |
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