| Year | Value | | 2022 | 1.1933419562345 | | 2021 | 1.2372989966631 | | 2020 | 1.3029199586405 | | 2019 | 1.3351385924559 | | 2018 | 1.3611313176273 | | 2017 | 1.387530074372 | | 2016 | 1.4108212130476 | | 2015 | 1.439893507279 | | 2014 | 1.4659679752485 | | 2013 | 1.4989864490543 | | 2012 | 1.5374688075605 | | 2011 | 1.1257472960688 | | 2010 | 1.1468886718608 | | 2009 | 1.6098133370454 | | 2008 | 1.6258560559591 | | 2007 | 1.6539902634844 | | 2006 | 1.6801616338611 | | 2005 | 1.6644855329909 | | 2004 | 1.6794164666167 | | 2003 | 1.7249002968363 | | 2002 | 1.744825137965 | | 2001 | 1.7959636591466 | | 2000 | 1.826141450326 | | 1999 | 1.8199209513648 | | 1998 | 1.8243292605552 | | 1997 | 1.8434943343862 | | 1996 | 1.861046656428 | | 1995 | 1.8689248646503 | | 1994 | 1.8898985779132 | | 1993 | 1.9264297907747 | | 1992 | 1.9581149086209 | | 1991 | 2.0116483894787 | | 1990 | 2.0595218245741 | | 1989 | 2.0732108425813 | | 1988 | 2.0772707868465 | | 1987 | 2.068650761003 | | 1986 | 2.053185771464 | | 1985 | 2.0316463548973 | | 1984 | 2.0168420476196 | | 1983 | 2.0219758105821 | | 1982 | 2.0191131257543 | | 1981 | 1.990462206484 | | 1980 | 1.9718429091104 | | 1979 | 1.9655008576631 | | 1978 | 1.9501210139487 | | 1977 | 1.9246445358751 | | 1976 | 1.8901292600723 | | 1975 | 1.849506970249 | | 1974 | 1.8040552409027 | | 1973 | 1.7887866637635 | | 1972 | 1.8025050521129 | | 1971 | 1.8124529257085 | | 1970 | 1.8145562237628 | | 1969 | 1.8141029322795 | | 1968 | 1.8172518849133 | | 1967 | 1.8158942299742 | | 1966 | 1.8221970306333 | | 1965 | 1.8416714610196 | | 1964 | 1.7813304871445 | | 1963 | 1.7807152172974 | | 1962 | 1.8586260287822 | | 1961 | 1.8739582415888 |
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