| Year | Value | | 2022 | 0.58501350492906 | | 2021 | 0.53599942969823 | | 2020 | 0.70557341465157 | | 2019 | 0.81751771972143 | | 2018 | 0.84932498219393 | | 2017 | 0.88447902988533 | | 2016 | 0.88891859336928 | | 2015 | 0.87003964246696 | | 2014 | 0.8555647989225 | | 2013 | 0.8962308711661 | | 2012 | 0.99668801239142 | | 2011 | 1.354002535262 | | 2010 | 1.6702609959916 | | 2009 | 1.6869151623893 | | 2008 | 1.7096216859332 | | 2007 | 1.7315892912895 | | 2006 | 1.7564131337566 | | 2005 | 1.7880117111529 | | 2004 | 1.8161659433917 | | 2003 | 1.8316372895431 | | 2002 | 1.7836924834135 | | 2001 | 1.734744900663 | | 2000 | 1.7700933000043 | | 1999 | 1.835112648882 | | 1998 | 1.8971603658691 | | 1997 | 1.9592993471422 | | 1996 | 2.0247742469179 | | 1995 | 2.1061649299799 | | 1994 | 2.2100598397478 | | 1993 | 1.9011619307231 | | 1992 | 1.4128916633666 | | 1991 | 1.3304881880807 | | 1990 | 1.393044137563 | | 1989 | 1.448208087335 | | 1988 | 1.497432072237 | | 1987 | 1.5449429624459 | | 1986 | 1.5974741619689 | | 1985 | 1.6517502433401 | | 1984 | 1.7098769599148 | | 1983 | 1.6029363570502 | | 1982 | 1.3094042280696 | | 1981 | 1.1479112098301 | | 1980 | 1.142329833939 | | 1979 | 1.1434805700935 | | 1978 | 1.1452810718478 | | 1977 | 1.156238125968 | | 1976 | 0.60068967574435 | | 1975 | 0.55706574416641 | | 1974 | 0.32633236327112 | | 1973 | 0.47522859161222 | | 1972 | 0.49642796834535 | | 1971 | 0.56161869725003 | | 1970 | 0.62350265585546 | | 1969 | 0.68842829794947 | | 1968 | 0.75499486907677 | | 1967 | 0.82047328880126 | | 1966 | 0.84216219675292 | | 1965 | 0.81436072081929 | | 1964 | 0.8637017469234 | | 1963 | 0.98944082431275 | | 1962 | 1.0576534413945 | | 1961 | 1.5326061360359 |
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