| Year | Value | | 2022 | 1.5290974439014 | | 2021 | 1.5411197657774 | | 2020 | 1.4761147388506 | | 2019 | 1.6239490260241 | | 2018 | 1.6076944720866 | | 2017 | 1.7244051778048 | | 2016 | 1.6647013038341 | | 2015 | 1.6712756502316 | | 2014 | 1.5486451405024 | | 2013 | 1.601318215305 | | 2012 | 1.1460185538286 | | 2011 | 1.1313091033043 | | 2010 | 1.0744572081554 | | 2009 | 1.0749106962104 | | 2008 | 0.95397855625097 | | 2007 | 0.77600826486264 | | 2006 | 0.69243000077562 | | 2005 | 0.64147846445718 | | 2004 | 0.68269275420646 | | 2003 | 0.99826492215956 | | 2002 | 0.80918751441936 | | 2001 | 0.82261051532863 | | 2000 | 0.72992906045894 | | 1993 | 1.1578297853585 | | 1991 | 1.5446855461567 | | 1990 | 2.2014836085188 | | 1989 | 2.6707954325527 | | 1988 | 2.8537455410226 | | 1987 | 2.950030102348 | | 1986 | 2.7701194696075 | | 1985 | 2.5827723588405 | | 1984 | 2.4404941247364 | | 1983 | 2.2749431264218 | | 1982 | 2.3075598415705 | | 1981 | 2.1457705266891 | | 1980 | 2.2213561964146 | | 1979 | 2.2395480225989 | | 1978 | 2.2696155871511 | | 1977 | 1.9047619047619 | | 1976 | 1.7581602373887 | | 1975 | 1.9039145907473 | | 1974 | 1.5988647114475 | | 1973 | 1.6833773087071 | | 1972 | 1.8360071301248 | | 1971 | 1.4700193423598 | | 1970 | 1.3692946058091 | | 1969 | 1.0682492581602 | | 1968 | 1.0854503464203 | | 1967 | 1.1371237458194 | | 1966 | 1.1818181818182 | | 1965 | 1.2291052114061 | | 1964 | 1.2800875273523 | | 1963 | 0.93170731707317 | | 1962 | 0.98838709677419 | | 1961 | 1.0758426966292 | | 1960 | 1.1684053651267 |
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