| Year | Value | | 2022 | 0.71763759810246 | | 2021 | 0.65056272603802 | | 2020 | 0.75047996526996 | | 2019 | 0.6895831041346 | | 2018 | 0.69399111009809 | | 2017 | 0.6660634439633 | | 2016 | 0.63403055291349 | | 2015 | 0.64367497823856 | | 2014 | 0.65143785554324 | | 2013 | 0.61182477304535 | | 2012 | 0.65315146197663 | | 2011 | 0.60292806014301 | | 2010 | 0.6675317048534 | | 2009 | 0.66746117027458 | | 2008 | 0.6998616571757 | | 2007 | 0.62761905715381 | | 2006 | 0.68342336067841 | | 2005 | 0.76653637179974 | | 2004 | 0.68761805213819 | | 2003 | 0.76414502712082 | | 2002 | 1.0589192112892 | | 2001 | 1.2134960521134 | | 2000 | 1.0300964715532 | | 1999 | 0.81624388755279 | | 1998 | 0.78006237414981 | | 1997 | 0.79692640682397 | | 1996 | 0.63365160997783 | | 1995 | 0.54947786760251 | | 1994 | 0.73376562403986 | | 1993 | 0.75507003635846 | | 1992 | 0.55908681609342 | | 1991 | 0.34815503222841 | | 1990 | 0.67572938756657 | | 1989 | 0.80036798528059 | | 1988 | 0.88004748786168 | | 1987 | 1.0181399417951 | | 1986 | 1.3441540546773 | | 1985 | 1.2100523506859 | | 1984 | 1.1988959806797 | | 1983 | 1.3665054334859 | | 1982 | 1.5820400783486 | | 1981 | 1.7201282527625 | | 1980 | 1.5835432156484 | | 1979 | 2.1822943187605 | | 1978 | 2.1755660696181 | | 1977 | 1.8857230058207 | | 1976 | 1.9283816272302 | | 1975 | 1.8310133088828 | | 1974 | 1.9650655021834 | | 1973 | 1.7912739369642 | | 1972 | 1.9875213847238 | | 1971 | 2.1962196219622 | | 1970 | 2.416694715584 | | 1969 | 2.6478244700632 | | 1968 | 3.2451713937707 | | 1967 | 3.1918687589158 | | 1966 | 3.4627199106395 | | 1965 | 4.2120704107293 | | 1964 | 3.7834950592006 | | 1963 | 3.8652130822597 | | 1962 | 4.3196544276458 | | 1961 | 5.229793977813 | | 1960 | 5.2315257478487 |
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