| Year | Value | | 2022 | 1.2179660152625 | | 2021 | 0.94184303932265 | | 2020 | 1.0184567859298 | | 2019 | 1.416846226768 | | 2018 | 1.5987861975766 | | 2017 | 1.7363813823682 | | 2016 | 1.9248202577229 | | 2015 | 2.0345195436659 | | 2014 | 1.9956178393202 | | 2013 | 1.8387138590316 | | 2012 | 1.6868664365985 | | 2011 | 1.5966124721345 | | 2010 | 1.7521932128014 | | 2009 | 2.0358367775224 | | 2008 | 2.1954203250079 | | 2007 | 2.205100068947 | | 2006 | 2.0147131800192 | | 2005 | 1.6700463394511 | | 2004 | 1.4865736626573 | | 2003 | 1.4662582094762 | | 2002 | 1.4974595018916 | | 2001 | 1.5274627109298 | | 2000 | 1.5970926587748 | | 1999 | 1.6369512705478 | | 1998 | 1.608963919856 | | 1997 | 1.6008168370929 | | 1996 | 1.5689826219328 | | 1995 | 1.4810329038402 | | 1994 | 1.5540990968448 | | 1993 | 1.4681748531546 | | 1992 | 1.5497873222728 | | 1991 | 1.9500168795487 | | 1990 | 2.0980301314765 | | 1989 | 2.1102894669348 | | 1988 | 1.9833703159688 | | 1987 | 2.0094008660972 | | 1986 | 2.0639683400519 | | 1985 | 2.065933128486 | | 1984 | 2.0307788671638 | | 1983 | 2.0444772930543 | | 1982 | 2.0254831485666 | | 1981 | 2.0110966639961 | | 1980 | 2.0400108125216 | | 1979 | 2.0769853369552 | | 1978 | 2.1628243706859 | | 1977 | 2.2011995316864 | | 1976 | 2.1619919389502 | | 1975 | 2.0989491848265 | | 1974 | 1.9947492612592 | | 1973 | 1.9439848163146 | | 1972 | 1.9110612636664 | | 1971 | 1.8785530515055 | | 1970 | 1.812980825788 | | 1969 | 1.8009220852956 | | 1968 | 1.8356973421858 | | 1967 | 1.7946000472328 | | 1966 | 1.7773889196668 | | 1965 | 1.8314811762897 | | 1964 | 1.9515655548394 | | 1963 | 2.0378924123729 | | 1962 | 2.046466141215 | | 1961 | 1.911873668318 |
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