| Year | Value | | 2022 | 0.3747295600227 | | 2021 | 0.40294521027492 | | 2020 | 0.43401730043456 | | 2019 | 0.4564468200879 | | 2018 | 0.47631509165105 | | 2017 | 0.49782120356208 | | 2016 | 0.51965435116521 | | 2015 | 0.5235150803579 | | 2014 | 0.49597980701513 | | 2013 | 0.45720640701651 | | 2012 | 0.41867480700165 | | 2011 | 0.39358675908281 | | 2010 | 0.42594088616934 | | 2009 | 0.45855625801703 | | 2008 | 0.46099303495839 | | 2007 | 0.49697310280054 | | 2006 | 0.55766831164137 | | 2005 | 0.63289401047263 | | 2004 | 0.70069747524257 | | 2003 | 0.60436980005948 | | 2002 | 0.53398433974718 | | 2001 | 0.62058347681743 | | 2000 | 0.69811563406068 | | 1999 | 0.78247987603986 | | 1998 | 0.85609544022829 | | 1997 | 0.93758581555624 | | 1996 | 1.0169491860177 | | 1995 | 1.2601030093017 | | 1994 | 1.5142555065591 | | 1993 | 1.5413534427023 | | 1992 | 1.5248938282132 | | 1991 | 1.5078924392255 | | 1990 | 1.4750807530757 | | 1989 | 1.4622194249923 | | 1988 | 1.4641711232866 | | 1987 | 1.4720791570524 | | 1986 | 1.4769754494515 | | 1985 | 1.4612108663707 | | 1984 | 1.4480222171304 | | 1983 | 1.4448927305982 | | 1982 | 1.4529634735116 | | 1981 | 1.4447105322217 | | 1980 | 1.4259579252198 | | 1979 | 1.4042237638246 | | 1978 | 1.3872317088009 | | 1977 | 1.4274309256634 | | 1976 | 1.5658266888005 | | 1975 | 1.7265073450918 | | 1974 | 1.8970556556611 | | 1973 | 2.2558865450061 | | 1972 | 2.4831910688547 | | 1971 | 2.5331567419194 | | 1970 | 2.644524356254 | | 1969 | 2.7007323903 | | 1968 | 2.8170778488229 | | 1967 | 2.7682286610455 | | 1966 | 2.5470459863898 | | 1965 | 2.4596090450946 | | 1964 | 2.472437061329 | | 1963 | 2.3908836459912 | | 1962 | 2.1911469716214 | | 1961 | 2.2132839405915 |
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