| Year | Value | | 2022 | 1.2971321635865 | | 2021 | 1.8749850100567 | | 2020 | 2.738391723519 | | 2019 | 3.7678727137557 | | 2018 | 4.0408295867712 | | 2017 | 4.0932849642137 | | 2016 | 4.5686164726404 | | 2015 | 4.3433416716518 | | 2014 | 4.0571918603049 | | 2013 | 4.6083525012511 | | 2012 | 4.0229918966585 | | 2011 | 3.6011951889012 | | 2010 | 3.9279922333951 | | 2009 | 4.1396550458289 | | 2008 | 4.2994142605737 | | 2007 | 4.4368706092381 | | 2006 | 4.6137286926137 | | 2005 | 4.8063193635962 | | 2004 | 5.0674399199205 | | 2003 | 5.3913898771432 | | 2002 | 5.0787496864371 | | 2001 | 4.3532785633744 | | 2000 | 4.1391227494214 | | 1999 | 4.2308214798439 | | 1998 | 4.2905200070089 | | 1997 | 4.3879444059969 | | 1996 | 4.5628647989132 | | 1995 | 4.7393880966977 | | 1994 | 4.9679324804856 | | 1993 | 5.1662059949026 | | 1992 | 5.4071490186377 | | 1991 | 5.1596434019828 | | 1990 | 4.2036185389945 | | 1989 | 3.7295072176034 | | 1988 | 3.9220713153281 | | 1987 | 4.0621694068909 | | 1986 | 4.1819721538935 | | 1985 | 4.386340445255 | | 1984 | 4.5533417707726 | | 1983 | 4.710740633185 | | 1982 | 4.8808117651959 | | 1981 | 4.6166989629964 | | 1980 | 3.5636724787975 | | 1979 | 3.0746086162309 | | 1978 | 3.2157111634531 | | 1977 | 3.2025167292071 | | 1976 | 3.3084807338443 | | 1975 | 3.181370660316 | | 1974 | 2.9392389460659 | | 1973 | 2.875490659925 | | 1972 | 2.6466573188163 | | 1971 | 1.3500687218903 | | 1970 | 0.035310734830168 | | 1969 | 0.08825346967661 | | 1968 | 0.10591351387261 | | 1967 | 0.17677218674268 | | 1966 | 0.035391966393138 | | 1965 | 0.14169325785451 | | 1964 | 0.14189431256236 | | 1963 | 0.017750954160389 | | 1962 | 0.14212118220931 | | 1961 | 0.37403196157232 |
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