| Year | Value | | 2022 | 2.9986091024237 | | 2021 | 3.1591049921429 | | 2020 | 3.3423209530181 | | 2019 | 3.0916992182135 | | 2018 | 3.2538669901796 | | 2017 | 3.2086551494565 | | 2016 | 3.2986212906233 | | 2015 | 3.4154897891262 | | 2014 | 3.3142932203991 | | 2013 | 3.3057467205825 | | 2012 | 3.4815723426151 | | 2011 | 3.5048160472237 | | 2010 | 3.5222996614616 | | 2009 | 3.2589743976486 | | 2008 | 3.1303317646665 | | 2007 | 3.2664970555269 | | 2006 | 1.968482469055 | | 2005 | 1.916786724108 | | 2004 | 1.5928522749924 | | 2003 | 1.77409007091 | | 2002 | 1.7458807289817 | | 2001 | 1.7623806012988 | | 1988 | 2.3370394593416 | | 1987 | 4.2054781886932 | | 1986 | 4.2076377772696 | | 1985 | 3.8807845327005 | | 1984 | 5.2108559498956 | | 1983 | 4.2406876790831 | | 1982 | 3.5170914838965 | | 1981 | 3.834808259587 | | 1980 | 3.2705649157582 | | 1979 | 3.5134239310573 | | 1978 | 3.3186725309876 | | 1977 | 3.2390412437918 | | 1976 | 3.8201663201663 | | 1975 | 3.9234149403641 | | 1974 | 4.9529124520405 | | 1973 | 5.0062578222778 | | 1972 | 4.5690550363448 |
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