| Year | Value | | 2022 | 1.5400306545719 | | 2021 | 1.4939670742411 | | 2020 | 1.5244546568749 | | 2019 | 1.3575571202997 | | 2018 | 1.3334553003809 | | 2017 | 1.3310617650367 | | 2016 | 1.3280635561863 | | 2015 | 1.3027895709386 | | 2014 | 1.3259089997724 | | 2013 | 1.3633421755313 | | 2012 | 1.4149910515894 | | 2011 | 1.4190662505919 | | 2010 | 1.4799492836561 | | 2009 | 1.5533048072383 | | 2008 | 1.465083851578 | | 2007 | 1.4273442306701 | | 2006 | 1.4698690525772 | | 2005 | 1.4679838675483 | | 2004 | 1.5579381133036 | | 2003 | 1.5739490111581 | | 2002 | 1.5765056540189 | | 2001 | 1.5914892186645 | | 2000 | 1.6396520522544 | | 1999 | 1.676053907821 | | 1998 | 1.7006345424403 | | 1997 | 1.7467037392786 | | 1996 | 1.7829746998094 | | 1995 | 1.7987480562344 | | 1994 | 1.9049192035598 | | 1993 | 1.9879279101391 | | 1992 | 2.0558396833191 | | 1991 | 2.1659757017272 | | 1990 | 2.3577041023744 | | 1989 | 2.425160069329 | | 1988 | 2.5262766404365 | | 1987 | 2.6341323725632 | | 1986 | 2.625576493961 | | 1985 | 2.6959551519114 | | 1984 | 2.7507885892676 | | 1983 | 2.8183111435352 | | 1982 | 2.8394952412631 | | 1981 | 2.799909702401 | | 1980 | 2.7185956376481 | | 1979 | 2.7623147693875 | | 1978 | 2.7925087443047 | | 1977 | 2.8133758486662 | | 1976 | 2.8000702722716 | | 1975 | 2.8714371372363 | | 1974 | 2.8295705276757 | | 1973 | 2.8039346912657 | | 1972 | 2.8921127805017 | | 1971 | 2.8425567269939 | | 1970 | 2.8393784140964 | | 1969 | 3.0230755467097 | | 1968 | 3.2737806229019 | | 1967 | 3.3107294748852 | | 1966 | 3.344864525096 | | 1965 | 3.3150574609282 | | 1964 | 3.4445634434787 | | 1963 | 3.5285443242512 | | 1962 | 3.7246820857944 | | 1961 | 3.7100112338332 | | 1960 | 3.8039003891139 |
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