| Year | Value | | 2022 | 1.8131566359467 | | 2021 | 1.8885407584761 | | 2020 | 1.7726547519841 | | 2019 | 1.6065123888413 | | 2018 | 1.5654235417162 | | 2017 | 1.5481209240583 | | 2016 | 1.5356138843772 | | 2015 | 1.4864835282364 | | 2014 | 1.4665434373358 | | 2013 | 1.5053923436021 | | 2012 | 1.5775376926931 | | 2011 | 1.7222020580758 | | 2010 | 1.8683572205221 | | 2009 | 1.9337434937545 | | 2008 | 1.9110717364553 | | 2007 | 1.8953363520329 | | 2006 | 1.9360292359912 | | 2005 | 1.9960742562538 | | 2004 | 2.0176408483871 | | 2003 | 2.0375419674609 | | 2002 | 2.0434645159218 | | 2001 | 1.9012933552948 | | 2000 | 1.7454947319822 | | 1999 | 1.7147172761384 | | 1998 | 1.7600520179466 | | 1997 | 1.7662299515255 | | 1996 | 1.6444595925835 | | 1995 | 1.5048662610399 | | 1994 | 1.4696826340889 | | 1993 | 1.5185585517638 | | 1992 | 1.668506732437 | | 1991 | 1.9613640821724 | | 1990 | 2.2725803020732 | | 1989 | 2.4202509931284 | | 1988 | 2.448825289288 | | 1987 | 2.4311676949236 | | 1986 | 2.3086953065226 | | 1985 | 2.0751089176396 | | 1984 | 1.8801873205244 | | 1983 | 1.8002343008935 | | 1982 | 1.7653359479904 | | 1981 | 1.7312638982597 | | 1980 | 1.7216068561869 | | 1979 | 0.51996091651798 | | 1978 | 0.71884289802433 | | 1977 | 0.69215943034434 | | 1976 | 0.60338241497697 | | 1975 | 0.45713237760004 | | 1974 | 0.58411861583476 | | 1973 | 1.6505649085073 | | 1972 | 1.8131374213609 | | 1971 | 1.8936170967874 | | 1970 | 1.9567962908696 | | 1969 | 1.4539532743146 | | 1968 | 0.94298487921958 | | 1967 | 1.0272623191111 | | 1966 | 1.8244350601964 | | 1965 | 2.5622990621191 | | 1964 | 2.5508809828924 | | 1963 | 2.5368303598756 | | 1962 | 2.5220444363198 | | 1961 | 2.4789458294783 |
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