| Year | Value | | 2022 | 6.5940967134185 | | 2021 | 2.8639104220499 | | 2020 | 0.8469055374593 | | 2019 | 1.6107678729038 | | 2018 | 1.9114009444569 | | 2017 | 1.9486474094453 | | 2016 | 1.2769909449732 | | 2015 | 1.5083667216592 | | 2014 | 2.487922705314 | | 2013 | 2.4498886414254 | | 2012 | 1.762780156132 | | 2011 | 3.3038501560874 | | 2010 | 2.9183400267738 | | 2009 | 1.7711171662125 | | 2008 | 4.3502985499005 | | 2007 | 2.3276112889148 | | 2006 | 3.5552877372703 | | 2005 | 2.6918316831683 | | 2004 | 2.3432552248258 | | 2003 | 2.7325959661679 | | 2002 | 2.9815745393635 | | 2001 | 4.4071353620147 | | 2000 | 4.4574351479722 | | 1999 | 1.4831294030404 | | 1998 | 0.86013462976814 | | 1997 | 0.22488755622189 | | 1996 | 2.6153846153846 | | 1995 | 4.6277665995976 | | 1994 | 1.9696347968814 | | 1993 | 1.7536534446764 | | 1992 | 1.0122311261071 | | 1991 | 3.1766753698868 | | 1990 | 7.3330219523587 | | 1989 | 7.5339025615269 | | 1988 | 7.2159396876683 | | 1987 | 8.5330216247808 | | 1986 | 9.0503505417463 | | 1985 | 6.734693877551 | | 1984 | 3.960396039604 | | 1983 | 10.038910505837 | | 1982 | 11.351819757366 | | 1981 | 9.4876660341556 | | 1980 | 10.135841170324 | | 1979 | 9.1220068415052 | | 1978 | 8.0049261083744 | | 1977 | 12.309820193638 | | 1976 | 13.322884012539 | | 1975 | 15.162454873646 | | 1974 | 15.416666666667 | | 1973 | 9.0909090909092 | | 1972 | 6.0240963855421 | | 1971 | 6.1381074168798 | | 1970 | 3.4391534391534 | | 1969 | 3.2786885245902 | | 1968 | 2.5210084033613 | | 1967 | 3.4782608695652 | | 1966 | 3.2934131736527 | | 1965 | 3.4055727554179 | | 1964 | 2.8662420382166 | | 1963 | 0.64102564102565 | | 1962 | 0.31948881789138 | | 1961 | 2.2875816993464 | | 1960 | 3.728813559322 |
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