| Year | Value | | 2022 | 1.8635111202225 | | 2021 | 1.7598292787753 | | 2020 | 1.9363915780619 | | 2019 | 1.8362978987182 | | 2018 | 1.8092869561814 | | 2017 | 1.8790670333413 | | 2016 | 1.9510985613662 | | 2015 | 1.9467362241317 | | 2014 | 1.9287924144785 | | 2013 | 1.915667289023 | | 2012 | 1.8749525049625 | | 2011 | 1.8271720096402 | | 2010 | 1.9018410900014 | | 2009 | 2.0492183946279 | | 2008 | 1.8669142866453 | | 2007 | 1.8534688453004 | | 2006 | 1.8910436035313 | | 2005 | 1.9260303539193 | | 2004 | 1.9315061340708 | | 2003 | 1.9869883621585 | | 2002 | 2.0176792492638 | | 2001 | 1.9723864019726 | | 2000 | 1.8943256481742 | | 1999 | 1.9691419747804 | | 1998 | 1.9065354044887 | | 1997 | 2.0513676590217 | | 1996 | 2.0666458446486 | | 1995 | 2.1489491068561 | | 1994 | 2.1977316439484 | | 1993 | 2.2209917062236 | | 1992 | 2.3816071565615 | | 1991 | 2.222901911066 | | 1990 | 2.5073866331001 | | 1989 | 2.7959927941006 | | 1987 | 3.4363203936629 | | 1986 | 3.4623076643207 | | 1985 | 3.268219396345 | | 1984 | 3.2289837880548 | | 1983 | 3.4828634205939 | | 1982 | 3.5342865242546 | | 1981 | 3.3885426555534 | | 1980 | 3.0275411069502 | | 1979 | 3.2647243913829 | | 1978 | 4.0494191233196 | | 1977 | 4.3714205866646 | | 1976 | 4.4704707233529 | | 1975 | 4.3973295046658 | | 1974 | 3.7699558111586 | | 1973 | 3.0443544781542 | | 1972 | 3.2599988156657 | | 1971 | 3.4847840196765 | | 1970 | 3.2907325866338 | | 1969 | 3.04980068175 | | 1968 | 3.03742341692 | | 1967 | 2.898879239174 | | 1965 | 3.1483614487122 | | 1964 | 2.955515643724 | | 1963 | 2.9716450747856 | | 1962 | 2.4866082709679 |
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